Perform Multi-Field Joins

This tutorial illustrates how to construct an aggregation pipeline, perform the aggregation on a collection, and display the results using the language of your choice.

About This Task

This tutorial demonstrates how to combine data from a collection that describes product information with another collection that describes customer orders. The results show a list of products ordered in 2020 and details about each order.

This aggregation performs a multi-field join by using $lookup. A multi-field join occurs when there are multiple corresponding fields in the documents of two collections. The aggregation matches these documents on the corresponding fields and combines information from both into one document.

Before You Begin

➤ Use the Select your language drop-down menu in the upper-right to set the language of the following examples or select MongoDB Shell.

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

An order can only contain one product. The aggregation uses a multi-field join to match a product document to documents representing orders of that product. The aggregation joins collections by the name and variation fields in documents in the products collection, corresponding to the product_name and product_variation fields in documents in the orders collection.

To create the orders and products collections, use the insertMany() method:

db.orders.deleteMany({})
db.orders.insertMany( [
   {
      customer_id: "elise_smith@myemail.com",
      orderdate: new Date("2020-05-30T08:35:52Z"),
      product_name: "Asus Laptop",
      product_variation: "Standard Display",
      value: 431.43,
   },
   {
      customer_id: "tj@wheresmyemail.com",
      orderdate: new Date("2019-05-28T19:13:32Z"),
      product_name: "The Day Of The Triffids",
      product_variation: "2nd Edition",
      value: 5.01,
   },
   {
      customer_id: "oranieri@warmmail.com",
      orderdate: new Date("2020-01-01T08:25:37Z"),
      product_name: "Morphy Richards Food Mixer",
      product_variation: "Deluxe",
      value: 63.13,
   },
   {
      customer_id: "jjones@tepidmail.com",
      orderdate: new Date("2020-12-26T08:55:46Z"),
      product_name: "Asus Laptop",
      product_variation: "Standard Display",
      value: 429.65,
   }
] )

db.products.deleteMany({})
db.products.insertMany( [
   {
      name: "Asus Laptop",
      variation: "Ultra HD",
      category: "ELECTRONICS",
      description: "Great for watching movies"
   },
   {
      name: "Asus Laptop",
      variation: "Standard Display",
      category: "ELECTRONICS",
      description: "Good value laptop for students"
   },
   {
      name: "The Day Of The Triffids",
      variation: "1st Edition",
      category: "BOOKS",
      description: "Classic post-apocalyptic novel"
   },
   {
      name: "The Day Of The Triffids",
      variation: "2nd Edition",
      category: "BOOKS",
      description: "Classic post-apocalyptic novel"
   },
   {
      name: "Morphy Richards Food Mixer",
      variation: "Deluxe",
      category: "KITCHENWARE",
      description: "Luxury mixer turning good cakes into great"
   }
] )

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new C app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Get Started with the C Driver guide.

To learn more about performing aggregations in the C Driver, see the Aggregation guide.

After you install the driver, create a file called agg-tutorial.c. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

#include <stdio.h>
#include <bson/bson.h>
#include <mongoc/mongoc.h>
int main(void)
{
    mongoc_init();
    // Replace the placeholder with your connection string.
    char *uri = "<connection string>";
    mongoc_client_t* client = mongoc_client_new(uri);
    // Get a reference to relevant collections.
    // ... mongoc_collection_t *some_coll = mongoc_client_get_collection(client, "agg_tutorials_db", "some_coll");
    // ... mongoc_collection_t *another_coll = mongoc_client_get_collection(client, "agg_tutorials_db", "another_coll");
    // Delete any existing documents in collections if needed.
    // ... {
    // ...     bson_t *filter = bson_new();
    // ...     bson_error_t error;
    // ...     if (!mongoc_collection_delete_many(some_coll, filter, NULL, NULL, &error))
    // ...     {
    // ...         fprintf(stderr, "Delete error: %s\n", error.message);
    // ...     }
    // ...     bson_destroy(filter);
    // ... }
    // Insert sample data into the collection or collections.
    // ... {
    // ...     size_t num_docs = ...;
    // ...     bson_t *docs[num_docs];
    // ...
    // ...     docs[0] = ...;
    // ...
    // ...     bson_error_t error;
    // ...     if (!mongoc_collection_insert_many(some_coll, (const bson_t **)docs, num_docs, NULL, NULL, &error))
    // ...     {
    // ...         fprintf(stderr, "Insert error: %s\n", error.message);
    // ...     }
    // ...
    // ...     for (int i = 0; i < num_docs; i++)
    // ...     {
    // ...         bson_destroy(docs[i]);
    // ...     }
    // ... }
    {
        const bson_t *doc;
        // Add code to create pipeline stages.
        bson_t *pipeline = BCON_NEW("pipeline", "[",
        // ... Add pipeline stages here.
        "]");
        // Run the aggregation.
        // ... mongoc_cursor_t *results = mongoc_collection_aggregate(some_coll, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
        bson_destroy(pipeline);
        // Print the aggregation results.
        while (mongoc_cursor_next(results, &doc))
        {
            char *str = bson_as_canonical_extended_json(doc, NULL);
            printf("%s\n", str);
            bson_free(str);
        }
        bson_error_t error;
        if (mongoc_cursor_error(results, &error))
        {
            fprintf(stderr, "Aggregation error: %s\n", error.message);
        }
        mongoc_cursor_destroy(results);
    }
    // Clean up resources.
    // ... mongoc_collection_destroy(some_coll);
    mongoc_client_destroy(client);
    mongoc_cleanup();
    return EXIT_SUCCESS;
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the C Get Started guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

char *uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

mongoc_collection_t *products = mongoc_client_get_collection(client, "agg_tutorials_db", "products");
mongoc_collection_t *orders = mongoc_client_get_collection(client, "agg_tutorials_db", "orders");
{
    bson_t *filter = bson_new();
    bson_error_t error;
    if (!mongoc_collection_delete_many(products, filter, NULL, NULL, &error))
    {
        fprintf(stderr, "Delete error: %s\n", error.message);
    }
    if (!mongoc_collection_delete_many(orders, filter, NULL, NULL, &error))
    {
        fprintf(stderr, "Delete error: %s\n", error.message);
    }
    bson_destroy(filter);
}
{
    size_t num_docs = 5;
    bson_t *product_docs[num_docs];
    product_docs[0] = BCON_NEW(
        "name", BCON_UTF8("Asus Laptop"),
        "variation", BCON_UTF8("Ultra HD"),
        "category", BCON_UTF8("ELECTRONICS"),
        "description", BCON_UTF8("Great for watching movies"));
    product_docs[1] = BCON_NEW(
        "name", BCON_UTF8("Asus Laptop"),
        "variation", BCON_UTF8("Standard Display"),
        "category", BCON_UTF8("ELECTRONICS"),
        "description", BCON_UTF8("Good value laptop for students"));
    product_docs[2] = BCON_NEW(
        "name", BCON_UTF8("The Day Of The Triffids"),
        "variation", BCON_UTF8("1st Edition"),
        "category", BCON_UTF8("BOOKS"),
        "description", BCON_UTF8("Classic post-apocalyptic novel"));
    product_docs[3] = BCON_NEW(
        "name", BCON_UTF8("The Day Of The Triffids"),
        "variation", BCON_UTF8("2nd Edition"),
        "category", BCON_UTF8("BOOKS"),
        "description", BCON_UTF8("Classic post-apocalyptic novel"));
    product_docs[4] = BCON_NEW(
        "name", BCON_UTF8("Morphy Richards Food Mixer"),
        "variation", BCON_UTF8("Deluxe"),
        "category", BCON_UTF8("KITCHENWARE"),
        "description", BCON_UTF8("Luxury mixer turning good cakes into great"));
    bson_error_t error;
    if (!mongoc_collection_insert_many(products, (const bson_t **)product_docs, num_docs, NULL, NULL, &error))
    {
        fprintf(stderr, "Insert error: %s\n", error.message);
    }
    for (int i = 0; i < num_docs; i++)
    {
        bson_destroy(product_docs[i]);
    }
}
{
    size_t num_docs = 4;
    bson_t *order_docs[num_docs];
    order_docs[0] = BCON_NEW(
        "customer_id", BCON_UTF8("elise_smith@myemail.com"),
        "orderdate", BCON_DATE_TIME(1590822952000UL), // 2020-05-30T08:35:52Z
        "product_name", BCON_UTF8("Asus Laptop"),
        "product_variation", BCON_UTF8("Standard Display"),
        "value", BCON_DOUBLE(431.43));
    order_docs[1] = BCON_NEW(
        "customer_id", BCON_UTF8("tj@wheresmyemail.com"),
        "orderdate", BCON_DATE_TIME(1559063612000UL), // 2019-05-28T19:13:32Z
        "product_name", BCON_UTF8("The Day Of The Triffids"),
        "product_variation", BCON_UTF8("2nd Edition"),
        "value", BCON_DOUBLE(5.01));
    order_docs[2] = BCON_NEW(
        "customer_id", BCON_UTF8("oranieri@warmmail.com"),
        "orderdate", BCON_DATE_TIME(1577869537000UL), // 2020-01-01T08:25:37Z
        "product_name", BCON_UTF8("Morphy Richards Food Mixer"),
        "product_variation", BCON_UTF8("Deluxe"),
        "value", BCON_DOUBLE(63.13));
    order_docs[3] = BCON_NEW(
        "customer_id", BCON_UTF8("jjones@tepidmail.com"),
        "orderdate", BCON_DATE_TIME(1608976546000UL), // 2020-12-26T08:55:46Z
        "product_name", BCON_UTF8("Asus Laptop"),
        "product_variation", BCON_UTF8("Standard Display"),
        "value", BCON_DOUBLE(429.65));
    bson_error_t error;
    if (!mongoc_collection_insert_many(orders, (const bson_t **)order_docs, num_docs, NULL, NULL, &error))
    {
        fprintf(stderr, "Insert error: %s\n", error.message);
    }
    for (int i = 0; i < num_docs; i++)
    {
        bson_destroy(order_docs[i]);
    }
}

Create the Template App

Before you begin following an aggregation tutorial, you must set up a new C++ app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Get Started with C++ tutorial.

To learn more about using the C++ driver, see the API documentation.

To learn more about performing aggregations in the C++ Driver, see the Aggregation guide.

After you install the driver, create a file called agg-tutorial.cpp. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

#include <iostream>
#include <bsoncxx/builder/basic/document.hpp>
#include <bsoncxx/builder/basic/kvp.hpp>
#include <bsoncxx/json.hpp>
#include <mongocxx/client.hpp>
#include <mongocxx/instance.hpp>
#include <mongocxx/pipeline.hpp>
#include <mongocxx/uri.hpp>
#include <chrono>
using bsoncxx::builder::basic::kvp;
using bsoncxx::builder::basic::make_document;
using bsoncxx::builder::basic::make_array;
int main() {
   mongocxx::instance instance;
   // Replace the placeholder with your connection string.
   mongocxx::uri uri("<connection string>");
   mongocxx::client client(uri);
   auto db = client["agg_tutorials_db"];
   // Delete existing data in the database, if necessary.
   db.drop();
   // Get a reference to relevant collections.
   // ... auto some_coll = db["..."];
   // ... auto another_coll = db["..."];
   // Insert sample data into the collection or collections.
   // ... some_coll.insert_many(docs);
   // Create an empty pipelne.
   mongocxx::pipeline pipeline;
   // Add code to create pipeline stages.
   // pipeline.match(make_document(...));
   // Run the aggregation and print the results.
   auto cursor = orders.aggregate(pipeline);
   for (auto&& doc : cursor) {
      std::cout << bsoncxx::to_json(doc, bsoncxx::ExtendedJsonMode::k_relaxed) << std::endl;
   }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the C++ Get Started tutorial.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

mongocxx::uri uri{"mongodb+srv://mongodb-example:27017"};

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

auto products = db["products"];
auto orders = db["orders"];
std::vector<bsoncxx::document::value> product_docs = {
    bsoncxx::from_json(R"({
        "name": "Asus Laptop",
        "variation": "Ultra HD",
        "category": "ELECTRONICS",
        "description": "Great for watching movies"
    })"),
    bsoncxx::from_json(R"({
        "name": "Asus Laptop",
        "variation": "Standard Display",
        "category": "ELECTRONICS",
        "description": "Good value laptop for students"
    })"),
    bsoncxx::from_json(R"({
        "name": "The Day Of The Triffids",
        "variation": "1st Edition",
        "category": "BOOKS",
        "description": "Classic post-apocalyptic novel"
    })"),
    bsoncxx::from_json(R"({
        "name": "The Day Of The Triffids",
        "variation": "2nd Edition",
        "category": "BOOKS",
        "description": "Classic post-apocalyptic novel"
    })"),
    bsoncxx::from_json(R"({
        "name": "Morphy Richards Food Mixer",
        "variation": "Deluxe",
        "category": "KITCHENWARE",
        "description": "Luxury mixer turning good cakes into great"
    })")
};
products.insert_many(product_docs); // Might throw an exception
std::vector<bsoncxx::document::value> order_docs = {
    bsoncxx::from_json(R"({
        "customer_id": "elise_smith@myemail.com",
        "orderdate": {"$date": 1590821752000},
        "product_name": "Asus Laptop",
        "product_variation": "Standard Display",
        "value": 431.43
    })"),
    bsoncxx::from_json(R"({
        "customer_id": "tj@wheresmyemail.com",
        "orderdate": {"$date": 1559062412000},
        "product_name": "The Day Of The Triffids",
        "product_variation": "2nd Edition",
        "value": 5.01
    })"),
    bsoncxx::from_json(R"({
        "customer_id": "oranieri@warmmail.com",
        "orderdate": {"$date": 1577861137000},
        "product_name": "Morphy Richards Food Mixer",
        "product_variation": "Deluxe",
        "value": 63.13
    })"),
    bsoncxx::from_json(R"({
        "customer_id": "jjones@tepidmail.com",
        "orderdate": {"$date": 1608972946000},
        "product_name": "Asus Laptop",
        "product_variation": "Standard Display",
        "value": 429.65
    })")
};
orders.insert_many(order_docs); // Might throw an exception

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new C#/.NET app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the C#/.NET Driver Quick Start guide.

To learn more about performing aggregations in the C#/.NET Driver, see the Aggregation guide.

After you install the driver, paste the following code into your Program.cs file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

using MongoDB.Driver;
using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;
// Define data model classes.
// ... public class MyClass { ... }
// Replace the placeholder with your connection string.
var uri = "<connection string>";
var client = new MongoClient(uri);
var aggDB = client.GetDatabase("agg_tutorials_db");
// Get a reference to relevant collections.
// ... var someColl = aggDB.GetCollection<MyClass>("someColl");
// ... var anotherColl = aggDB.GetCollection<MyClass>("anotherColl");
// Delete any existing documents in collections if needed.
// ... someColl.DeleteMany(Builders<MyClass>.Filter.Empty);
// Insert sample data into the collection or collections.
// ... someColl.InsertMany(new List<MyClass> { ... });
// Add code to chain pipeline stages to the Aggregate() method.
// ... var results = someColl.Aggregate().Match(...);
// Print the aggregation results.
foreach (var result in results.ToList())
{
  Console.WriteLine(result);
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Set Up a Free Tier Cluster in Atlas step of the C# Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

var uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

An order can only contain one product. The aggregation uses a multi-field join to match a product document to documents representing orders of that product. The aggregation joins collections by the Name and Variation fields in documents in the products collection, corresponding to the ProductName and ProductVariation fields in documents in the orders collection.

First, create C# classes to model the data in the products and orders collections:

public class Product
{
  [BsonId]
  public ObjectId Id { get; set; }
  public string Name { get; set; }
  public string Variation { get; set; }
  public string Category { get; set; }
  public string Description { get; set; }
}
public class Order
{
  [BsonId]
  public ObjectId Id { get; set; }
  public string CustomerId { get; set; }
  public DateTime OrderDate { get; set; }
  public string ProductName { get; set; }
  public string ProductVariation { get; set; }
  public double Value { get; set; }
}

To create the products and orders collections and insert the sample data, add the following code to your application:

var products = aggDB.GetCollection<Product>("products");
var orders = aggDB.GetCollection<Order>("orders");
products.DeleteMany(Builders<Product>.Filter.Empty);
orders.DeleteMany(Builders<Order>.Filter.Empty);
products.InsertMany(new List<Product>
{
    new Product
    {
        Name = "Asus Laptop",
        Variation = "Ultra HD",
        Category = "ELECTRONICS",
        Description = "Great for watching movies"
    },
    new Product
    {
        Name = "Asus Laptop",
        Variation = "Standard Display",
        Category = "ELECTRONICS",
        Description = "Good value laptop for students"
    },
    new Product
    {
        Name = "The Day Of The Triffids",
        Variation = "1st Edition",
        Category = "BOOKS",
        Description = "Classic post-apocalyptic novel"
    },
    new Product
    {
        Name = "The Day Of The Triffids",
        Variation = "2nd Edition",
        Category = "BOOKS",
        Description = "Classic post-apocalyptic novel"
    },
    new Product
    {
        Name = "Morphy Richards Food Mixer",
        Variation = "Deluxe",
        Category = "KITCHENWARE",
        Description = "Luxury mixer turning good cakes into great"
    }
});
orders.InsertMany(new List<Order>
{
    new Order
    {
        CustomerId = "elise_smith@myemail.com",
        OrderDate = DateTime.Parse("2020-05-30T08:35:52Z"),
        ProductName = "Asus Laptop",
        ProductVariation = "Standard Display",
        Value = 431.43
    },
    new Order
    {
        CustomerId = "tj@wheresmyemail.com",
        OrderDate = DateTime.Parse("2019-05-28T19:13:32Z"),
        ProductName = "The Day Of The Triffids",
        ProductVariation = "2nd Edition",
        Value = 5.01
    },
    new Order
    {
        CustomerId = "oranieri@warmmail.com",
        OrderDate = DateTime.Parse("2020-01-01T08:25:37Z"),
        ProductName = "Morphy Richards Food Mixer",
        ProductVariation = "Deluxe",
        Value = 63.13
    },
    new Order
    {
        CustomerId = "jjones@tepidmail.com",
        OrderDate = DateTime.Parse("2020-12-26T08:55:46Z"),
        ProductName = "Asus Laptop",
        ProductVariation = "Standard Display",
        Value = 429.65
    }
});

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new Go app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Go Driver Quick Start guide.

To learn more about performing aggregations in the Go Driver, see the Aggregation guide.

After you install the driver, create a file called agg_tutorial.go. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

package main
import (
    "context"
    "fmt"
    "log"
    "time"
    "go.mongodb.org/mongo-driver/v2/bson"
    "go.mongodb.org/mongo-driver/v2/mongo"
    "go.mongodb.org/mongo-driver/v2/mongo/options"
)
// Define structs.
// type MyStruct struct { ... }
func main() {
    // Replace the placeholder with your connection string.
    const uri = "<connection string>"
    client, err := mongo.Connect(options.Client().ApplyURI(uri))
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = client.Disconnect(context.TODO()); err != nil {
            log.Fatal(err)
        }
    }()
    aggDB := client.Database("agg_tutorials_db")
    // Get a reference to relevant collections.
    // ... someColl := aggDB.Collection("...")
    // ... anotherColl := aggDB.Collection("...")
    // Delete any existing documents in collections if needed.
    // ... someColl.DeleteMany(context.TODO(), bson.D{})
    // Insert sample data into the collection or collections.
    // ... _, err = someColl.InsertMany(...)
    // Add code to create pipeline stages.
    // ... myStage := bson.D{{...}}
    // Create a pipeline that includes the stages.
    // ... pipeline := mongo.Pipeline{...}
    // Run the aggregation.
    // ... cursor, err := someColl.Aggregate(context.TODO(), pipeline)
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err := cursor.Close(context.TODO()); err != nil {
            log.Fatalf("failed to close cursor: %v", err)
        }
    }()
    // Decode the aggregation results.
    var results []bson.D
    if err = cursor.All(context.TODO(), &results); err != nil {
        log.Fatalf("failed to decode results: %v", err)
    }
    // Print the aggregation results.
    for _, result := range results {
        res, _ := bson.MarshalExtJSON(result, false, false)
        fmt.Println(string(res))
    }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a MongoDB Cluster step of the Go Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

const uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

First, create Go structs to model the data in the products and orders collections:

type Product struct {
	Name        string
	Variation   string
	Category    string
	Description string
}
type Order struct {
	CustomerID       string        `bson:"customer_id"`
	OrderDate        bson.DateTime `bson:"orderdate"`
	ProductName      string        `bson:"product_name"`
	ProductVariation string        `bson:"product_variation"`
	Value            float32       `bson:"value"`
}

To create the products and orders collections and insert the sample data, add the following code to your application:

products := aggDB.Collection("products")
orders := aggDB.Collection("orders")
products.DeleteMany(context.TODO(), bson.D{})
orders.DeleteMany(context.TODO(), bson.D{})
_, err = products.InsertMany(context.TODO(), []interface{}{
	Product{
		Name:        "Asus Laptop",
		Variation:   "Ultra HD",
		Category:    "ELECTRONICS",
		Description: "Great for watching movies",
	},
	Product{
		Name:        "Asus Laptop",
		Variation:   "Standard Display",
		Category:    "ELECTRONICS",
		Description: "Good value laptop for students",
	},
	Product{
		Name:        "The Day Of The Triffids",
		Variation:   "1st Edition",
		Category:    "BOOKS",
		Description: "Classic post-apocalyptic novel",
	},
	Product{
		Name:        "The Day Of The Triffids",
		Variation:   "2nd Edition",
		Category:    "BOOKS",
		Description: "Classic post-apocalyptic novel",
	},
	Product{
		Name:        "Morphy Richards Food Mixer",
		Variation:   "Deluxe",
		Category:    "KITCHENWARE",
		Description: "Luxury mixer turning good cakes into great",
	},
})
if err != nil {
	log.Fatal(err)
}
_, err = orders.InsertMany(context.TODO(), []interface{}{
	Order{
		CustomerID:       "elise_smith@myemail.com",
		OrderDate:        bson.NewDateTimeFromTime(time.Date(2020, 5, 30, 8, 35, 52, 0, time.UTC)),
		ProductName:      "Asus Laptop",
		ProductVariation: "Standard Display",
		Value:            431.43,
	},
	Order{
		CustomerID:       "tj@wheresmyemail.com",
		OrderDate:        bson.NewDateTimeFromTime(time.Date(2019, 5, 28, 19, 13, 32, 0, time.UTC)),
		ProductName:      "The Day Of The Triffids",
		ProductVariation: "2nd Edition",
		Value:            5.01,
	},
	Order{
		CustomerID:       "oranieri@warmmail.com",
		OrderDate:        bson.NewDateTimeFromTime(time.Date(2020, 1, 1, 8, 25, 37, 0, time.UTC)),
		ProductName:      "Morphy Richards Food Mixer",
		ProductVariation: "Deluxe",
		Value:            63.13,
	},
	Order{
		CustomerID:       "jjones@tepidmail.com",
		OrderDate:        bson.NewDateTimeFromTime(time.Date(2020, 12, 26, 8, 55, 46, 0, time.UTC)),
		ProductName:      "Asus Laptop",
		ProductVariation: "Standard Display",
		Value:            429.65,
	},
})
if err != nil {
	log.Fatal(err)
}

Create the Template App

Before you begin following an aggregation tutorial, you must set up a new Java app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Get Started with the Java Driver guide.

To learn more about performing aggregations in the Java Sync Driver, see the Aggregation guide.

After you install the driver, create a file called AggTutorial.java. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

package org.example;
// Modify imports for each tutorial as needed.
import com.mongodb.client.*;
import com.mongodb.client.model.Aggregates;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Sorts;
import org.bson.Document;
import org.bson.conversions.Bson;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class AggTutorial {
    public static void main( String[] args ) {
        // Replace the placeholder with your connection string.
        String uri = "<connection string>";
        try (MongoClient mongoClient = MongoClients.create(uri)) {
            MongoDatabase aggDB = mongoClient.getDatabase("agg_tutorials_db");
            // Get a reference to relevant collections.
            // ... MongoCollection<Document> someColl = ...
            // ... MongoCollection<Document> anotherColl = ...
            // Delete any existing documents in collections if needed.
            // ... someColl.deleteMany(Filters.empty());
            // Insert sample data into the collection or collections.
            // ... someColl.insertMany(...);
            // Create an empty pipeline array.
            List<Bson> pipeline = new ArrayList<>();
            // Add code to create pipeline stages.
            // ... pipeline.add(...);
            // Run the aggregation.
            // ... AggregateIterable<Document> aggregationResult = someColl.aggregate(pipeline);
            // Print the aggregation results.
            for (Document document : aggregationResult) {
                System.out.println(document.toJson());
            }
        }
    }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Java Sync Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

String uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

MongoCollection<Document> products = aggDB.getCollection("products");
MongoCollection<Document> orders = aggDB.getCollection("orders");
products.deleteMany(Filters.empty());
orders.deleteMany(Filters.empty());
products.insertMany(
        Arrays.asList(
                new Document("name", "Asus Laptop")
                        .append("variation", "Ultra HD")
                        .append("category", "ELECTRONICS")
                        .append("description", "Great for watching movies"),
                new Document("name", "Asus Laptop")
                        .append("variation", "Standard Display")
                        .append("category", "ELECTRONICS")
                        .append("description", "Good value laptop for students"),
                new Document("name", "The Day Of The Triffids")
                        .append("variation", "1st Edition")
                        .append("category", "BOOKS")
                        .append("description", "Classic post-apocalyptic novel"),
                new Document("name", "The Day Of The Triffids")
                        .append("variation", "2nd Edition")
                        .append("category", "BOOKS")
                        .append("description", "Classic post-apocalyptic novel"),
                new Document("name", "Morphy Richards Food Mixer")
                        .append("variation", "Deluxe")
                        .append("category", "KITCHENWARE")
                        .append("description", "Luxury mixer turning good cakes into great")
        )
);
orders.insertMany(
        Arrays.asList(
                new Document("customer_id", "elise_smith@myemail.com")
                        .append("orderdate", LocalDateTime.parse("2020-05-30T08:35:52"))
                        .append("product_name", "Asus Laptop")
                        .append("product_variation", "Standard Display")
                        .append("value", 431.43),
                new Document("customer_id", "tj@wheresmyemail.com")
                        .append("orderdate", LocalDateTime.parse("2019-05-28T19:13:32"))
                        .append("product_name", "The Day Of The Triffids")
                        .append("product_variation", "2nd Edition")
                        .append("value", 5.01),
                new Document("customer_id", "oranieri@warmmail.com")
                        .append("orderdate", LocalDateTime.parse("2020-01-01T08:25:37"))
                        .append("product_name", "Morphy Richards Food Mixer")
                        .append("product_variation", "Deluxe")
                        .append("value", 63.13),
                new Document("customer_id", "jjones@tepidmail.com")
                        .append("orderdate", LocalDateTime.parse("2020-12-26T08:55:46"))
                        .append("product_name", "Asus Laptop")
                        .append("product_variation", "Standard Display")
                        .append("value", 429.65)
        )
);

Create the Template App

Tip

To learn how to install the driver and connect to MongoDB, see the Get Started with the Java Driver guide.

To learn more about performing aggregations in the Java Sync Driver, see the Aggregation guide.

After you install the driver, create a file called AggTutorial.java. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

package org.example;
// Modify imports for each tutorial as needed.
import com.mongodb.client.*;
import com.mongodb.client.model.Aggregates;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Sorts;
import org.bson.Document;
import org.bson.conversions.Bson;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class AggTutorial {
    public static void main( String[] args ) {
        // Replace the placeholder with your connection string.
        String uri = "<connection string>";
        try (MongoClient mongoClient = MongoClients.create(uri)) {
            MongoDatabase aggDB = mongoClient.getDatabase("agg_tutorials_db");
            // Get a reference to relevant collections.
            // ... MongoCollection<Document> someColl = ...
            // ... MongoCollection<Document> anotherColl = ...
            // Delete any existing documents in collections if needed.
            // ... someColl.deleteMany(Filters.empty());
            // Insert sample data into the collection or collections.
            // ... someColl.insertMany(...);
            // Create an empty pipeline array.
            List<Bson> pipeline = new ArrayList<>();
            // Add code to create pipeline stages.
            // ... pipeline.add(...);
            // Run the aggregation.
            // ... AggregateIterable<Document> aggregationResult = someColl.aggregate(pipeline);
            // Print the aggregation results.
            for (Document document : aggregationResult) {
                System.out.println(document.toJson());
            }
        }
    }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Java Sync Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

String uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

First, create Kotlin data classes to model the data in the products and orders collections:

@Serializable
data class Product(
    val name: String,
    val variation: String,
    val category: String,
    val description: String
)
@Serializable
data class Order(
    val customerID: String,
    @Contextual val orderDate: LocalDateTime,
    val productName: String,
    val productVariation: String,
    val value: Double
)

To create the products and orders collections and insert the sample data, add the following code to your application:

val products = aggDB.getCollection<Product>("products")
val orders = aggDB.getCollection<Order>("orders")
products.deleteMany(Filters.empty());
orders.deleteMany(Filters.empty());
products.insertMany(
    listOf(
        Product("Asus Laptop", "Ultra HD", "ELECTRONICS", "Great for watching movies"),
        Product("Asus Laptop", "Standard Display", "ELECTRONICS", "Good value laptop for students"),
        Product("The Day Of The Triffids", "1st Edition", "BOOKS", "Classic post-apocalyptic novel"),
        Product("The Day Of The Triffids", "2nd Edition", "BOOKS", "Classic post-apocalyptic novel"),
        Product(
            "Morphy Richards Food Mixer",
            "Deluxe",
            "KITCHENWARE",
            "Luxury mixer turning good cakes into great"
        )
    )
)
orders.insertMany(
    listOf(
        Order(
            "elise_smith@myemail.com",
            LocalDateTime.parse("2020-05-30T08:35:52"),
            "Asus Laptop",
            "Standard Display",
            431.43
        ),
        Order(
            "tj@wheresmyemail.com",
            LocalDateTime.parse("2019-05-28T19:13:32"),
            "The Day Of The Triffids",
            "2nd Edition",
            5.01
        ),
        Order(
            "oranieri@warmmail.com",
            LocalDateTime.parse("2020-01-01T08:25:37"),
            "Morphy Richards Food Mixer",
            "Deluxe",
            63.13
        ),
        Order(
            "jjones@tepidmail.com",
            LocalDateTime.parse("2020-12-26T08:55:46"),
            "Asus Laptop",
            "Standard Display",
            429.65
        )
    )
)

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new Node.js app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Node.js Driver Quick Start guide.

To learn more about performing aggregations in the Node.js Driver, see the Aggregation guide.

After you install the driver, create a file called agg_tutorial.js. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

const { MongoClient } = require("mongodb");
// Replace the placeholder with your connection string.
const uri = "<connection string>";
const client = new MongoClient(uri);
async function run() {
  try {
    const aggDB = client.db("agg_tutorials_db");
    // Get a reference to relevant collections.
    // ... const someColl =
    // ... const anotherColl =
    // Delete any existing documents in collections.
    // ... await someColl.deleteMany({});
    // Insert sample data into the collection or collections.
    // ... const someData = [ ... ];
    // ... await someColl.insertMany(someData);
    // Create an empty pipeline array.
    const pipeline = [];
    // Add code to create pipeline stages.
    // ... pipeline.push({ ... })
    // Run the aggregation.
    // ... const aggregationResult = ...
    // Print the aggregation results.
    for await (const document of aggregationResult) {
      console.log(document);
    }
  } finally {
    await client.close();
  }
}
run().catch(console.dir);

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Node.js Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

const uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

const products = aggDB.collection("products");
const orders = aggDB.collection("orders");
await products.deleteMany({});
await orders.deleteMany({});
await products.insertMany([
  {
    name: "Asus Laptop",
    variation: "Ultra HD",
    category: "ELECTRONICS",
    description: "Great for watching movies",
  },
  {
    name: "Asus Laptop",
    variation: "Standard Display",
    category: "ELECTRONICS",
    description: "Good value laptop for students",
  },
  {
    name: "The Day Of The Triffids",
    variation: "1st Edition",
    category: "BOOKS",
    description: "Classic post-apocalyptic novel",
  },
  {
    name: "The Day Of The Triffids",
    variation: "2nd Edition",
    category: "BOOKS",
    description: "Classic post-apocalyptic novel",
  },
  {
    name: "Morphy Richards Food Mixer",
    variation: "Deluxe",
    category: "KITCHENWARE",
    description: "Luxury mixer turning good cakes into great",
  },
]);
await orders.insertMany([
  {
    customer_id: "elise_smith@myemail.com",
    orderdate: new Date("2020-05-30T08:35:52Z"),
    product_name: "Asus Laptop",
    product_variation: "Standard Display",
    value: 431.43,
  },
  {
    customer_id: "tj@wheresmyemail.com",
    orderdate: new Date("2019-05-28T19:13:32Z"),
    product_name: "The Day Of The Triffids",
    product_variation: "2nd Edition",
    value: 5.01,
  },
  {
    customer_id: "oranieri@warmmail.com",
    orderdate: new Date("2020-01-01T08:25:37Z"),
    product_name: "Morphy Richards Food Mixer",
    product_variation: "Deluxe",
    value: 63.13,
  },
  {
    customer_id: "jjones@tepidmail.com",
    orderdate: new Date("2020-12-26T08:55:46Z"),
    product_name: "Asus Laptop",
    product_variation: "Standard Display",
    value: 429.65,
  },
]);

Create the Template App

Tip

To learn how to install the driver and connect to MongoDB, see the Go Driver Quick Start guide.

To learn more about performing aggregations in the Go Driver, see the Aggregation guide.

After you install the driver, create a file called agg_tutorial.go. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

package main
import (
    "context"
    "fmt"
    "log"
    "time"
    "go.mongodb.org/mongo-driver/v2/bson"
    "go.mongodb.org/mongo-driver/v2/mongo"
    "go.mongodb.org/mongo-driver/v2/mongo/options"
)
// Define structs.
// type MyStruct struct { ... }
func main() {
    // Replace the placeholder with your connection string.
    const uri = "<connection string>"
    client, err := mongo.Connect(options.Client().ApplyURI(uri))
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = client.Disconnect(context.TODO()); err != nil {
            log.Fatal(err)
        }
    }()
    aggDB := client.Database("agg_tutorials_db")
    // Get a reference to relevant collections.
    // ... someColl := aggDB.Collection("...")
    // ... anotherColl := aggDB.Collection("...")
    // Delete any existing documents in collections if needed.
    // ... someColl.DeleteMany(context.TODO(), bson.D{})
    // Insert sample data into the collection or collections.
    // ... _, err = someColl.InsertMany(...)
    // Add code to create pipeline stages.
    // ... myStage := bson.D{{...}}
    // Create a pipeline that includes the stages.
    // ... pipeline := mongo.Pipeline{...}
    // Run the aggregation.
    // ... cursor, err := someColl.Aggregate(context.TODO(), pipeline)
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err := cursor.Close(context.TODO()); err != nil {
            log.Fatalf("failed to close cursor: %v", err)
        }
    }()
    // Decode the aggregation results.
    var results []bson.D
    if err = cursor.All(context.TODO(), &results); err != nil {
        log.Fatalf("failed to decode results: %v", err)
    }
    // Print the aggregation results.
    for _, result := range results {
        res, _ := bson.MarshalExtJSON(result, false, false)
        fmt.Println(string(res))
    }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a MongoDB Cluster step of the Go Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

const uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

$products = $client->agg_tutorials_db->products;
$orders = $client->agg_tutorials_db->orders;
$products->deleteMany([]);
$orders->deleteMany([]);
$products->insertMany(
    [
        [
            'name' => "Asus Laptop",
            'variation' => "Ultra HD",
            'category' => "ELECTRONICS",
            'description' => "Great for watching movies"
        ],
        [
            'name' => "Asus Laptop",
            'variation' => "Standard Display",
            'category' => "ELECTRONICS",
            'description' => "Good value laptop for students"
        ],
        [
            'name' => "The Day Of The Triffids",
            'variation' => "1st Edition",
            'category' => "BOOKS",
            'description' => "Classic post-apocalyptic novel"
        ],
        [
            'name' => "The Day Of The Triffids",
            'variation' => "2nd Edition",
            'category' => "BOOKS",
            'description' => "Classic post-apocalyptic novel"
        ],
        [
            'name' => "Morphy Richards Food Mixer",
            'variation' => "Deluxe",
            'category' => "KITCHENWARE",
            'description' => "Luxury mixer turning good cakes into great"
        ]
    ]
);
$orders->insertMany(
    [
        [
            'customer_id' => "elise_smith@myemail.com",
            'orderdate' => new UTCDateTime((new DateTimeImmutable("2020-05-30T08:35:52"))),
            'product_name' => "Asus Laptop",
            'product_variation' => "Standard Display",
            'value' => 431.43
        ],
        [
            'customer_id' => "tj@wheresmyemail.com",
            'orderdate' => new UTCDateTime((new DateTimeImmutable("2019-05-28T19:13:32"))),
            'product_name' => "The Day Of The Triffids",
            'product_variation' => "2nd Edition",
            'value' => 5.01
        ],
        [
            'customer_id' => "oranieri@warmmail.com",
            'orderdate' => new UTCDateTime((new DateTimeImmutable("2020-01-01T08:25:37"))),
            'product_name' => "Morphy Richards Food Mixer",
            'product_variation' => "Deluxe",
            'value' => 63.13
        ],
        [
            'customer_id' => "jjones@tepidmail.com",
            'orderdate' => new UTCDateTime((new DateTimeImmutable("2020-12-26T08:55:46"))),
            'product_name' => "Asus Laptop",
            'product_variation' => "Standard Display",
            'value' => 429.65
        ]
    ]
);

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new Python app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install PyMongo and connect to MongoDB, see the Get Started with PyMongo tutorial.

To learn more about performing aggregations in PyMongo, see the Aggregation guide.

After you install the library, create a file called agg_tutorial.py. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

# Modify imports for each tutorial as needed.
from pymongo import MongoClient
# Replace the placeholder with your connection string.
uri = "<connection string>"
client = MongoClient(uri)
try:
    agg_db = client["agg_tutorials_db"]
    # Get a reference to relevant collections.
    # ... some_coll = agg_db["some_coll"]
    # ... another_coll = agg_db["another_coll"]
    # Delete any existing documents in collections if needed.
    # ... some_coll.delete_many({})
    # Insert sample data into the collection or collections.
    # ... some_coll.insert_many(...)
    # Create an empty pipeline array.
    pipeline = []
    # Add code to create pipeline stages.
    # ... pipeline.append({...})
    # Run the aggregation.
    # ... aggregation_result = ...
    # Print the aggregation results.
    for document in aggregation_result:
        print(document)
finally:
    client.close()

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Get Started with the PHP Library tutorial.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

uri = "mongodb+srv://mongodb-example:27017"

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

products_coll = agg_db["products"]
orders_coll = agg_db["orders"]
products_coll.delete_many({})
products_data = [
    {
        "name": "Asus Laptop",
        "variation": "Ultra HD",
        "category": "ELECTRONICS",
        "description": "Great for watching movies",
    },
    {
        "name": "Asus Laptop",
        "variation": "Standard Display",
        "category": "ELECTRONICS",
        "description": "Good value laptop for students",
    },
    {
        "name": "The Day Of The Triffids",
        "variation": "1st Edition",
        "category": "BOOKS",
        "description": "Classic post-apocalyptic novel",
    },
    {
        "name": "The Day Of The Triffids",
        "variation": "2nd Edition",
        "category": "BOOKS",
        "description": "Classic post-apocalyptic novel",
    },
    {
        "name": "Morphy Richards Food Mixer",
        "variation": "Deluxe",
        "category": "KITCHENWARE",
        "description": "Luxury mixer turning good cakes into great",
    },
]
products_coll.insert_many(products_data)

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new Ruby app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the Ruby Driver and connect to MongoDB, see the Get Started with the Ruby Driver guide.

To learn more about performing aggregations in the Ruby Driver, see the Aggregation guide.

After you install the driver, create a file called agg_tutorial.rb. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

# typed: strict
require 'mongo'
require 'bson'
# Replace the placeholder with your connection string.
uri = "<connection string>"
Mongo::Client.new(uri) do |client|
  agg_db = client.use('agg_tutorials_db')
  # Get a reference to relevant collections.
  # ... some_coll = agg_db[:some_coll]
  # Delete any existing documents in collections if needed.
  # ... some_coll.delete_many({})
  # Insert sample data into the collection or collections.
  # ... some_coll.insert_many( ... )
  # Add code to create pipeline stages within the array.
  # ... pipeline = [ ... ]
  # Run the aggregation.
  # ... aggregation_result = some_coll.aggregate(pipeline)
  # Print the aggregation results.
  aggregation_result.each do |doc|
    puts doc
  end
end

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Ruby Get Started guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

uri = "mongodb+srv://mongodb-example:27017"

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

products = agg_db[:products]
orders = agg_db[:orders]
products.delete_many({})
orders.delete_many({})
products.insert_many(
  [
    {
      name: "Asus Laptop",
      variation: "Ultra HD",
      category: "ELECTRONICS",
      description: "Great for watching movies",
    },
    {
      name: "Asus Laptop",
      variation: "Standard Display",
      category: "ELECTRONICS",
      description: "Good value laptop for students",
    },
    {
      name: "The Day Of The Triffids",
      variation: "1st Edition",
      category: "BOOKS",
      description: "Classic post-apocalyptic novel",
    },
    {
      name: "The Day Of The Triffids",
      variation: "2nd Edition",
      category: "BOOKS",
      description: "Classic post-apocalyptic novel",
    },
    {
      name: "Morphy Richards Food Mixer",
      variation: "Deluxe",
      category: "KITCHENWARE",
      description: "Luxury mixer turning good cakes into great",
    },
  ]
)
orders.insert_many(
  [
    {
      customer_id: "elise_smith@myemail.com",
      orderdate: DateTime.parse("2020-05-30T08:35:52Z"),
      product_name: "Asus Laptop",
      product_variation: "Standard Display",
      value: 431.43,
    },
    {
      customer_id: "tj@wheresmyemail.com",
      orderdate: DateTime.parse("2019-05-28T19:13:32Z"),
      product_name: "The Day Of The Triffids",
      product_variation: "2nd Edition",
      value: 5.01,
    },
    {
      customer_id: "oranieri@warmmail.com",
      orderdate: DateTime.parse("2020-01-01T08:25:37Z"),
      product_name: "Morphy Richards Food Mixer",
      product_variation: "Deluxe",
      value: 63.13,
    },
    {
      customer_id: "jjones@tepidmail.com",
      orderdate: DateTime.parse("2020-12-26T08:55:46Z"),
      product_name: "Asus Laptop",
      product_variation: "Standard Display",
      value: 429.65,
    },
  ]
)

Create the Template App

Before you begin following this aggregation tutorial, you must set up a new Rust app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Rust Driver Quick Start guide.

To learn more about performing aggregations in the Rust Driver, see the Aggregation guide.

After you install the driver, create a file called agg-tutorial.rs. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

use mongodb::{
    bson::{doc, Document},
    options::ClientOptions,
    Client,
};
use futures::stream::TryStreamExt;
use std::error::Error;
// Define structs.
// #[derive(Debug, Serialize, Deserialize)]
// struct MyStruct { ... }
#[tokio::main]
async fn main() mongodb::error::Result<()> {
    // Replace the placeholder with your connection string.
    let uri = "<connection string>";
    let client = Client::with_uri_str(uri).await?;
    let agg_db = client.database("agg_tutorials_db");
    // Get a reference to relevant collections.
    // ... let some_coll: Collection<T> = agg_db.collection("...");
    // ... let another_coll: Collection<T> = agg_db.collection("...");
    // Delete any existing documents in collections if needed.
    // ... some_coll.delete_many(doc! {}).await?;
    // Insert sample data into the collection or collections.
    // ... some_coll.insert_many(vec![...]).await?;
    // Create an empty pipeline.
    let mut pipeline = Vec::new();
    // Add code to create pipeline stages.
    // pipeline.push(doc! { ... });
    // Run the aggregation and print the results.
    let mut results = some_coll.aggregate(pipeline).await?;
    while let Some(result) = results.try_next().await? {
       println!("{:?}\n", result);
    }
    Ok(())
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Rust Quick Start guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

let uri = "mongodb+srv://mongodb-example:27017";

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

First, create Rust structs to model the data in the products and orders collections:

#[derive(Debug, Serialize, Deserialize)]
struct Product {
    name: String,
    variation: String,
    category: String,
    description: String,
}
#[derive(Debug, Serialize, Deserialize)]
struct Order {
    customer_id: String,
    order_date: DateTime,
    product_name: String,
    product_variation: String,
    value: f32,
}

To create the products and orders collections and insert the sample data, add the following code to your application:

let products: Collection<Product> = agg_db.collection("products");
let orders: Collection<Order> = agg_db.collection("orders");
products.delete_many(doc! {}).await?;
orders.delete_many(doc! {}).await?;
let product_docs = vec![
    Product {
        name: "Asus Laptop".to_string(),
        variation: "Ultra HD".to_string(),
        category: "ELECTRONICS".to_string(),
        description: "Great for watching movies".to_string(),
    },
    Product {
        name: "Asus Laptop".to_string(),
        variation: "Standard Display".to_string(),
        category: "ELECTRONICS".to_string(),
        description: "Good value laptop for students".to_string(),
    },
    Product {
        name: "The Day Of The Triffids".to_string(),
        variation: "1st Edition".to_string(),
        category: "BOOKS".to_string(),
        description: "Classic post-apocalyptic novel".to_string(),
    },
    Product {
        name: "The Day Of The Triffids".to_string(),
        variation: "2nd Edition".to_string(),
        category: "BOOKS".to_string(),
        description: "Classic post-apocalyptic novel".to_string(),
    },
    Product {
        name: "Morphy Richards Food Mixer".to_string(),
        variation: "Deluxe".to_string(),
        category: "KITCHENWARE".to_string(),
        description: "Luxury mixer turning good cakes into great".to_string(),
    },
];
products.insert_many(product_docs).await?;
let order_docs = vec![
    Order {
        customer_id: "elise_smith@myemail.com".to_string(),
        order_date: DateTime::builder().year(2020).month(5).day(30).hour(8).minute(35).second(52).build().unwrap(),
        product_name: "Asus Laptop".to_string(),
        product_variation: "Standard Display".to_string(),
        value: 431.43,
    },
    Order {
        customer_id: "tj@wheresmyemail.com".to_string(),
        order_date: DateTime::builder().year(2019).month(5).day(28).hour(19).minute(13).second(32).build().unwrap(),
        product_name: "The Day Of The Triffids".to_string(),
        product_variation: "2nd Edition".to_string(),
        value: 5.01,
    },
    Order {
        customer_id: "oranieri@warmmail.com".to_string(),
        order_date: DateTime::builder().year(2020).month(1).day(1).hour(8).minute(25).second(37).build().unwrap(),
        product_name: "Morphy Richards Food Mixer".to_string(),
        product_variation: "Deluxe".to_string(),
        value: 63.13,
    },
    Order {
        customer_id: "jjones@tepidmail.com".to_string(),
        order_date: DateTime::builder().year(2020).month(12).day(26).hour(8).minute(55).second(46).build().unwrap(),
        product_name: "Asus Laptop".to_string(),
        product_variation: "Standard Display".to_string(),
        value: 429.65,
    },
];
orders.insert_many(order_docs).await?;

Create the Template App

Before you begin following an aggregation tutorial, you must set up a new Scala app. You can use this app to connect to a MongoDB deployment, insert sample data into MongoDB, and run the aggregation pipeline.

Tip

To learn how to install the driver and connect to MongoDB, see the Get Started with the Scala Driver guide.

To learn more about performing aggregations in the Scala Driver, see the Aggregation guide.

After you install the driver, create a file called AggTutorial.scala. Paste the following code in this file to create an app template for the aggregation tutorials.

Important

In the following code, read the code comments to find the sections of the code that you must modify for the tutorial you are following.

If you attempt to run the code without making any changes, you will encounter a connection error.

package org.example;
// Modify imports for each tutorial as needed.
import org.mongodb.scala.MongoClient
import org.mongodb.scala.bson.Document
import org.mongodb.scala.model.{Accumulators, Aggregates, Field, Filters, Variable}
import java.text.SimpleDateFormat
object FilteredSubset {
  def main(args: Array[String]): Unit = {
    // Replace the placeholder with your connection string.
    val uri = "<connection string>"
    val mongoClient = MongoClient(uri)
    Thread.sleep(1000)
    val aggDB = mongoClient.getDatabase("agg_tutorials_db")
    // Get a reference to relevant collections.
    // ... val someColl = aggDB.getCollection("someColl")
    // ... val anotherColl = aggDB.getCollection("anotherColl")
    // Delete any existing documents in collections if needed.
    // ... someColl.deleteMany(Filters.empty()).subscribe(...)
    // If needed, create the date format template.
    val dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")
    // Insert sample data into the collection or collections.
    // ... someColl.insertMany(...).subscribe(...)
    Thread.sleep(1000)
    // Add code to create pipeline stages within the Seq.
    // ... val pipeline = Seq(...)
    // Run the aggregation and print the results.
    // ... someColl.aggregate(pipeline).subscribe(...)
    Thread.sleep(1000)
    mongoClient.close()
  }
}

For every tutorial, you must replace the connection string placeholder with your deployment's connection string.

Tip

To learn how to locate your deployment's connection string, see the Create a Connection String step of the Scala Driver Get Started guide.

For example, if your connection string is "mongodb+srv://mongodb-example:27017", your connection string assignment resembles the following:

val uri = "mongodb+srv://mongodb-example:27017"

Create the Collection

This example uses two collections:

products, which contains documents describing the products that a shop sells
orders, which contains documents describing individual orders for products in a shop

To create the products and orders collections and insert the sample data, add the following code to your application:

val products = aggDB.getCollection("products")
val orders = aggDB.getCollection("orders")
products.deleteMany(Filters.empty()).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)
orders.deleteMany(Filters.empty()).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)
val dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")
products.insertMany(
  Seq(
    Document(
      "name" -> "Asus Laptop",
      "variation" -> "Ultra HD",
      "category" -> "ELECTRONICS",
      "description" -> "Great for watching movies"
    ),
    Document(
      "name" -> "Asus Laptop",
      "variation" -> "Standard Display",
      "category" -> "ELECTRONICS",
      "description" -> "Good value laptop for students"
    ),
    Document(
      "name" -> "The Day Of The Triffids",
      "variation" -> "1st Edition",
      "category" -> "BOOKS",
      "description" -> "Classic post-apocalyptic novel"
    ),
    Document(
      "name" -> "The Day Of The Triffids",
      "variation" -> "2nd Edition",
      "category" -> "BOOKS",
      "description" -> "Classic post-apocalyptic novel"
    ),
    Document(
      "name" -> "Morphy Richards Food Mixer",
      "variation" -> "Deluxe",
      "category" -> "KITCHENWARE",
      "description" -> "Luxury mixer turning good cakes into great"
    )
  )
).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)
orders.insertMany(
  Seq(
    Document(
      "customer_id" -> "elise_smith@myemail.com",
      "orderdate" -> dateFormat.parse("2020-05-30T08:35:52"),
      "product_name" -> "Asus Laptop",
      "product_variation" -> "Standard Display",
      "value" -> 431.43
    ),
    Document(
      "customer_id" -> "tj@wheresmyemail.com",
      "orderdate" -> dateFormat.parse("2019-05-28T19:13:32"),
      "product_name" -> "The Day Of The Triffids",
      "product_variation" -> "2nd Edition",
      "value" -> 5.01
    ),
    Document(
      "customer_id" -> "oranieri@warmmail.com",
      "orderdate" -> dateFormat.parse("2020-01-01T08:25:37"),
      "product_name" -> "Morphy Richards Food Mixer",
      "product_variation" -> "Deluxe",
      "value" -> 63.13
    ),
    Document(
      "customer_id" -> "jjones@tepidmail.com",
      "orderdate" -> dateFormat.parse("2020-12-26T08:55:46"),
      "product_name" -> "Asus Laptop",
      "product_variation" -> "Standard Display",
      "value" -> 429.65
    )
  )
).subscribe(
  _ => {},
  e => println("Error: " + e.getMessage),
)

Steps

The following steps demonstrate how to create and run an aggregation pipeline to join collections on multiple fields.

Create an embedded pipeline to use in the lookup stage.

The first stage of the pipeline is a $lookup stage to join the orders collection to the products collection by two fields in each collection. The $lookup stage contains an embedded pipeline to configure the join.

embedded_pl = [
   // Stage 1: Match the values of two fields on each side of the join
   // The $eq filter uses aliases for the name and variation fields set
   { $match: {
      $expr: {
         $and: [
            { $eq: ["$product_name", "$$prdname"] },
            { $eq: ["$product_variation", "$$prdvartn"] }
         ]
      }
   } },
   // Stage 2: Match orders placed in 2020
   { $match: {
      orderdate: {
         $gte: new Date("2020-01-01T00:00:00Z"),
         $lt: new Date("2021-01-01T00:00:00Z")
      }
   } },
   // Stage 3: Remove unneeded fields from the orders collection side of the join
   { $unset: ["_id", "product_name", "product_variation"] }
]

Run the aggregation pipeline.

db.products.aggregate( [
   // Use the embedded pipeline in a lookup stage
   { $lookup: {
         from: "orders",
         let: {
            prdname: "$name",
            prdvartn: "$variation"
         },
         pipeline: embedded_pl,
         as: "orders"
   } },
   // Match products ordered in 2020
   { $match: { orders: { $ne: [] } } },
   // Remove unneeded fields
   { $unset: ["_id", "description"] }
] )

Interpret the aggregation results.

The aggregated results contain two documents. The documents represent products ordered 2020. Each document contains an orders array field that lists details about each order for that product.

{
   name: 'Asus Laptop',
   variation: 'Standard Display',
   category: 'ELECTRONICS',
   orders: [
      {
         customer_id: 'elise_smith@myemail.com',
         orderdate: ISODate('2020-05-30T08:35:52.000Z'),
         value: 431.43
      },
      {
         customer_id: 'jjones@tepidmail.com',
         orderdate: ISODate('2020-12-26T08:55:46.000Z'),
         value: 429.65
      }
   ]
}
{
   name: 'Morphy Richards Food Mixer',
   variation: 'Deluxe',
   category: 'KITCHENWARE',
   orders: [
      {
         customer_id: 'oranieri@warmmail.com',
         orderdate: ISODate('2020-01-01T08:25:37.000Z'),
         value: 63.13
      }
   ]
}

Add a lookup stage to link the collections and import fields.

The first stage of the pipeline is a $lookup stage to join the orders collection to the products collection by two fields in each collection. The lookup stage contains an embedded pipeline to configure the join.

Create the embedded pipeline, then add a $match stage to match the values of two fields on each side of the join. Note that the following code uses aliases for the name and variation fields set when creating the $lookup stage:

bson_t embedded_pipeline;
bson_array_builder_t *bab = bson_array_builder_new();
bson_array_builder_append_document(bab, BCON_NEW(
                                            "$match", "{",
                                            "$expr", "{", "$and",
                                            "[",
                                            "{", "$eq", "[", BCON_UTF8("$product_name"), BCON_UTF8("$$prdname"), "]", "}",
                                            "{", "$eq", "[", BCON_UTF8("$product_variation"), BCON_UTF8("$$prdvartn"), "]", "}",
                                            "]",
                                            "}",
                                            "}"));

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

bson_array_builder_append_document(bab, BCON_NEW(
                                            "$match", "{", "orderdate",
                                            "{",
                                            "$gte", BCON_DATE_TIME(1577836800000UL),
                                            "$lt", BCON_DATE_TIME(1609459200000UL),
                                            "}",
                                            "}"));

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

bson_array_builder_append_document(bab, BCON_NEW(
                                            "$unset",
                                            "[", BCON_UTF8("_id"), BCON_UTF8("product_name"), BCON_UTF8("product_variation"),
                                            "]"));
// Builds the embedded pipeline array and cleans up resources
bson_array_builder_build(bab, &embedded_pipeline);
bson_array_builder_destroy(bab);

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

"{", "$lookup", "{",
"from", BCON_UTF8("orders"),
"let", "{",
"prdname", BCON_UTF8("$name"),
"prdvartn", BCON_UTF8("$variation"),
"}",
"pipeline", BCON_ARRAY(&embedded_pipeline),
"as", BCON_UTF8("orders"),
"}", "}",

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

"{",
"$match", "{",
"orders", "{", "$ne", "[", "]", "}",
"}", "}",

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

"{", "$unset", "[", BCON_UTF8("_id"), BCON_UTF8("description"), "]", "}",

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

mongoc_cursor_t *results =
    mongoc_collection_aggregate(products, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
bson_destroy(&embedded_pipeline);
bson_destroy(pipeline);

Ensure that you clean up the collection resources by adding the following line to your cleanup statements:

mongoc_collection_destroy(products);
mongoc_collection_destroy(orders);

Finally, run the following commands in your shell to generate and run the executable:

gcc -o aggc agg-tutorial.c $(pkg-config --libs --cflags libmongoc-1.0)
./aggc

Tip

If you encounter connection errors by running the preceding commands in one call, you can run them separately.

Interpret the aggregation results.

The aggregated result contains two documents. The documents represent products for which there were orders placed in 2020. Each document contains an orders array field that lists details about each order for that product:

{ "name" : "Asus Laptop", "variation" : "Standard Display", "category" : "ELECTRONICS", "orders" : [ { "customer_id" : "elise_smith@myemail.com", "orderdate" : { "$date" : { "$numberLong" : "1590822952000" } }, "value" : { "$numberDouble" : "431.43000000000000682" } }, { "customer_id" : "jjones@tepidmail.com", "orderdate" : { "$date" : { "$numberLong" : "1608976546000" } }, "value" : { "$numberDouble" : "429.64999999999997726" } } ] }
{ "name" : "Morphy Richards Food Mixer", "variation" : "Deluxe", "category" : "KITCHENWARE", "orders" : [ { "customer_id" : "oranieri@warmmail.com", "orderdate" : { "$date" : { "$numberLong" : "1577869537000" } }, "value" : { "$numberDouble" : "63.130000000000002558" } } ] }

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

Within the embedded pipeline, add a $match stage to match the values of two fields on each side of the join. Note that the following code uses aliases for the name and variation fields set when creating the $lookup stage:

auto embed_match_stage1 = bsoncxx::from_json(R"({
    "$match": {
        "$expr": {
            "$and": [
                { "$eq": ["$product_name", "$$prdname"] },
                { "$eq": ["$product_variation", "$$prdvartn"] }
            ]
        }
    }
})");

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

auto embed_match_stage2 = bsoncxx::from_json(R"({
    "$match": {
        "orderdate": {
            "$gte": { "$date": 1577836800000 },
            "$lt": { "$date": 1609459200000 }
        }
    }
})");

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

auto embed_unset_stage = bsoncxx::from_json(R"({
    "$unset": ["_id", "product_name", "product_variation"]
})");

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

pipeline.lookup(make_document(
    kvp("from", "orders"),
    kvp("let", make_document(
        kvp("prdname", "$name"),
        kvp("prdvartn", "$variation")
    )),
    kvp("pipeline", make_array(embed_match_stage1, embed_match_stage2, embed_unset_stage)),
    kvp("as", "orders")
));

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

pipeline.match(bsoncxx::from_json(R"({
    "orders": { "$ne": [] }
})"));

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

pipeline.append_stage(bsoncxx::from_json(R"({
    "$unset": ["_id", "description"]
})"));

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

auto cursor = products.aggregate(pipeline);

Finally, run the following command in your shell to start your application:

c++ --std=c++17 agg-tutorial.cpp $(pkg-config --cflags --libs libmongocxx) -o ./app.out
./app.out

Interpret the aggregation results.

{ "name" : "Asus Laptop", "variation" : "Standard Display", "category" : "ELECTRONICS",
"orders" : [ { "customer_id" : "elise_smith@myemail.com", "orderdate" : { "$date" : "2020-05-30T06:55:52Z" },
"value" : 431.43000000000000682 }, { "customer_id" : "jjones@tepidmail.com", "orderdate" : { "$date" :
"2020-12-26T08:55:46Z" }, "value" : 429.64999999999997726 } ] }
{ "name" : "Morphy Richards Food Mixer", "variation" : "Deluxe", "category" : "KITCHENWARE",
"orders" : [ { "customer_id" : "oranieri@warmmail.com", "orderdate" : { "$date" : "2020-01-01T06:45:37Z" },
"value" : 63.130000000000002558 } ] }

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

Instantiate the embedded pipeline, then chain a $match stage to match the values of two fields on each side of the join. Note that the following code uses aliases for the Name and Variation fields set when creating the $lookup stage:

var embeddedPipeline = new EmptyPipelineDefinition<Order>()
    .Match(new BsonDocument("$expr",
        new BsonDocument("$and", new BsonArray
        {
                new BsonDocument("$eq", new BsonArray { "$ProductName", "$$prdname" }),
                new BsonDocument("$eq", new BsonArray { "$ProductVariation", "$$prdvartn" })
        })))

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

.Match(o => o.OrderDate >= DateTime.Parse("2020-01-01T00:00:00Z") &&
            o.OrderDate < DateTime.Parse("2021-01-01T00:00:00Z"))

Within the embedded pipeline, add a $project stage to remove unneeded fields from the orders collection side of the join:

.Project(Builders<Order>.Projection
        .Exclude(o => o.Id)
        .Exclude(o => o.ProductName)
        .Exclude(o => o.ProductVariation));

After the embedded pipeline is completed, start the main aggregation on the products collection and chain the $lookup stage. Configure this stage to store the processed lookup fields in an array field called Orders:

var results = products.Aggregate()
    .Lookup<Order, BsonDocument, IEnumerable<BsonDocument>, BsonDocument>(
        foreignCollection: orders,
        let: new BsonDocument { { "prdname", "$Name" }, { "prdvartn", "$Variation" } },
        lookupPipeline: embeddedPipeline,
        "Orders"
    )

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the Orders array created in the previous step:

.Match(Builders<BsonDocument>.Filter.Ne("Orders", new BsonArray()))

Add a projection stage to remove unneeded fields.

Finally, add a $project stage. The $project stage removes the _id and Description fields from the result documents:

.Project(Builders<BsonDocument>.Projection
    .Exclude("_id")
    .Exclude("Description")
);

Run the aggregation and interpret the results.

Finally, run the application in your IDE and inspect the results.

The aggregated result contains two documents. The documents represent products for which there were orders placed in 2020. Each document contains an Orders array field that lists details about each order for that product:

{ "Name" : "Asus Laptop", "Variation" : "Standard Display", "Category" : "ELECTRONICS", "Orders" : [{ "CustomerId" : "elise_smith@myemail.com", "OrderDate" : { "$date" : "2020-05-30T08:35:52Z" }, "Value" : 431.43000000000001 }, { "CustomerId" : "jjones@tepidmail.com", "OrderDate" : { "$date" : "2020-12-26T08:55:46Z" }, "Value" : 429.64999999999998 }] }
{ "Name" : "Morphy Richards Food Mixer", "Variation" : "Deluxe", "Category" : "KITCHENWARE", "Orders" : [{ "CustomerId" : "oranieri@warmmail.com", "OrderDate" : { "$date" : "2020-01-01T08:25:37Z" }, "Value" : 63.130000000000003 }] }

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

embeddedMatchStage1 := bson.D{
	{Key: "$match", Value: bson.D{
		{Key: "$expr", Value: bson.D{
			{Key: "$and", Value: bson.A{
				bson.D{{Key: "$eq", Value: bson.A{"$product_name", "$$prdname"}}},
				bson.D{{Key: "$eq", Value: bson.A{"$product_variation", "$$prdvartn"}}},
			}},
		}},
	}},
}

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

embeddedMatchStage2 := bson.D{
	{Key: "$match", Value: bson.D{
		{Key: "orderdate", Value: bson.D{
			{Key: "$gte", Value: time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)},
			{Key: "$lt", Value: time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC)},
		}},
	}},
}

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

embeddedUnsetStage := bson.D{
	{Key: "$unset", Value: bson.A{"_id", "product_name", "product_variation"}},
}

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

embeddedPipeline := mongo.Pipeline{embeddedMatchStage1, embeddedMatchStage2, embeddedUnsetStage}
lookupStage := bson.D{
	{Key: "$lookup", Value: bson.D{
		{Key: "from", Value: "orders"},
		{Key: "let", Value: bson.D{
			{Key: "prdname", Value: "$name"},
			{Key: "prdvartn", Value: "$variation"},
		}},
		{Key: "pipeline", Value: embeddedPipeline},
		{Key: "as", Value: "orders"},
	}},
}

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

matchStage := bson.D{
	{Key: "$match", Value: bson.D{
		{Key: "orders", Value: bson.D{{Key: "$ne", Value: bson.A{}}}},
	}},
}

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

unsetStage := bson.D{
	{Key: "$unset", Value: bson.A{"_id", "description"}},
}

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

pipeline := mongo.Pipeline{lookupStage, matchStage, unsetStage}
cursor, err := products.Aggregate(context.TODO(), pipeline)

Finally, run the following command in your shell to start your application:

go run agg_tutorial.go

Interpret the aggregation results.

{"name":"Asus Laptop","variation":"Standard Display","category":"ELECTRONICS","orders":[{"customer_id":"elise_smith@myemail.com","orderdate":{"$date":"2020-05-30T08:35:52Z"},"value":431.42999267578125},{"customer_id":"jjones@tepidmail.com","orderdate":{"$date":"2020-12-26T08:55:46Z"},"value":429.6499938964844}]}
{"name":"Morphy Richards Food Mixer","variation":"Deluxe","category":"KITCHENWARE","orders":[{"customer_id":"oranieri@warmmail.com","orderdate":{"$date":"2020-01-01T08:25:37Z"},"value":63.130001068115234}]}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

List<Bson> embeddedPipeline = new ArrayList<>();
embeddedPipeline.add(Aggregates.match(
        Filters.expr(
                Filters.and(
                        new Document("$eq", Arrays.asList("$product_name", "$$prdname")),
                        new Document("$eq", Arrays.asList("$product_variation", "$$prdvartn"))
                )
        )
));

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

embeddedPipeline.add(Aggregates.match(Filters.and(
        Filters.gte("orderdate", LocalDateTime.parse("2020-01-01T00:00:00")),
        Filters.lt("orderdate", LocalDateTime.parse("2021-01-01T00:00:00"))
)));

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

embeddedPipeline.add(Aggregates.unset("_id", "product_name", "product_variation"));

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

pipeline.add(Aggregates.lookup(
        "orders",
        Arrays.asList(
                new Variable<>("prdname", "$name"),
                new Variable<>("prdvartn", "$variation")
        ),
        embeddedPipeline,
        "orders"
));

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

pipeline.add(Aggregates.match(
        Filters.ne("orders", new ArrayList<>())
));

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

pipeline.add(Aggregates.unset("_id", "description"));

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

AggregateIterable<Document> aggregationResult = products.aggregate(pipeline);

Finally, run the application in your IDE.

Interpret the aggregation results.

{"name": "Asus Laptop", "variation": "Standard Display", "category": "ELECTRONICS", "orders": [{"customer_id": "elise_smith@myemail.com", "orderdate": {"$date": "2020-05-30T08:35:52Z"}, "value": 431.43}, {"customer_id": "jjones@tepidmail.com", "orderdate": {"$date": "2020-12-26T08:55:46Z"}, "value": 429.65}]}
{"name": "Morphy Richards Food Mixer", "variation": "Deluxe", "category": "KITCHENWARE", "orders": [{"customer_id": "oranieri@warmmail.com", "orderdate": {"$date": "2020-01-01T08:25:37Z"}, "value": 63.13}]}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

val embeddedPipeline = mutableListOf<Bson>()
embeddedPipeline.add(
    Aggregates.match(
        Filters.expr(
            Document(
                "\$and", listOf(
                    Document("\$eq", listOf("\$${Order::productName.name}", "$\$prdname")),
                    Document("\$eq", listOf("\$${Order::productVariation.name}", "$\$prdvartn"))
                )
            )
        )
    )
)

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

embeddedPipeline.add(
    Aggregates.match(
        Filters.and(
            Filters.gte(
                Order::orderDate.name,
                LocalDateTime.parse("2020-01-01T00:00:00").toJavaLocalDateTime()
            ),
            Filters.lt(Order::orderDate.name, LocalDateTime.parse("2021-01-01T00:00:00").toJavaLocalDateTime())
        )
    )
)

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

embeddedPipeline.add(Aggregates.unset("_id", Order::productName.name, Order::productVariation.name))

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

pipeline.add(
    Aggregates.lookup(
        "orders",
        listOf(
            Variable("prdname", "\$${Product::name.name}"),
            Variable("prdvartn", "\$${Product::variation.name}")
        ),
        embeddedPipeline,
        "orders"
    )
)

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

pipeline.add(
    Aggregates.match(
        Filters.ne("orders", mutableListOf<Document>())
    )
)

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

pipeline.add(Aggregates.unset("_id", "description"))

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

val aggregationResult = products.aggregate<Document>(pipeline)

Finally, run the application in your IDE.

Interpret the aggregation results.

Document{{name=Asus Laptop, variation=Standard Display, category=ELECTRONICS, orders=[Document{{customerID=elise_smith@myemail.com, orderDate=Sat May 30 04:35:52 EDT 2020, value=431.43}}, Document{{customerID=jjones@tepidmail.com, orderDate=Sat Dec 26 03:55:46 EST 2020, value=429.65}}]}}
Document{{name=Morphy Richards Food Mixer, variation=Deluxe, category=KITCHENWARE, orders=[Document{{customerID=oranieri@warmmail.com, orderDate=Wed Jan 01 03:25:37 EST 2020, value=63.13}}]}}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

const embedded_pl = [];
embedded_pl.push({
  $match: {
    $expr: {
      $and: [
        { $eq: ["$product_name", "$$prdname"] },
        { $eq: ["$product_variation", "$$prdvartn"] },
      ],
    },
  },
});

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

embedded_pl.push({
  $match: {
    orderdate: {
      $gte: new Date("2020-01-01T00:00:00Z"),
      $lt: new Date("2021-01-01T00:00:00Z"),
    },
  },
});

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

embedded_pl.push({
  $unset: ["_id", "product_name", "product_variation"],
});

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

pipeline.push({
  $lookup: {
    from: "orders",
    let: {
      prdname: "$name",
      prdvartn: "$variation",
    },
    pipeline: embedded_pl,
    as: "orders",
  },
});

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

pipeline.push({
  $match: {
    orders: { $ne: [] },
  },
});

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

pipeline.push({
  $unset: ["_id", "description"],
});

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

const aggregationResult = await products.aggregate(pipeline);

Finally, run the following command in your shell to start your application:

node agg_tutorial.js

Interpret the aggregation results.

{
  name: 'Asus Laptop',
  variation: 'Standard Display',
  category: 'ELECTRONICS',
  orders: [
    {
      customer_id: 'elise_smith@myemail.com',
      orderdate: 2020-05-30T08:35:52.000Z,
      value: 431.43
    },
    {
      customer_id: 'jjones@tepidmail.com',
      orderdate: 2020-12-26T08:55:46.000Z,
      value: 429.65
    }
  ]
}
{
  name: 'Morphy Richards Food Mixer',
  variation: 'Deluxe',
  category: 'KITCHENWARE',
  orders: [
    {
      customer_id: 'oranieri@warmmail.com',
      orderdate: 2020-01-01T08:25:37.000Z,
      value: 63.13
    }
  ]
}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

$embeddedPipeline = new Pipeline(
    // Add stages within embedded pipeline.
};

Stage::match(
    Query::expr(
        Expression::and(
            Expression::eq(
                Expression::stringFieldPath('product_name'),
                Expression::variable('prdname')
            ),
            Expression::eq(
                Expression::stringFieldPath('product_variation'),
                Expression::variable('prdvartn')
            ),
        )
    )
),

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

Stage::match(
    orderdate: [
        Query::gte(new UTCDateTime(new DateTimeImmutable('2020-01-01T00:00:00'))),
        Query::lt(new UTCDateTime(new DateTimeImmutable('2021-01-01T00:00:00'))),
    ]
),

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

Stage::unset('_id', 'product_name', 'product_variation')

Next, outside of your Pipeline instances, create the $lookup stage in a factory function. Configure this stage to store the processed lookup fields in an array field called orders:

function lookupOrdersStage(Pipeline $embeddedPipeline)
{
    return Stage::lookup(
        from: 'orders',
        let: object(
            prdname: Expression::stringFieldPath('name'),
            prdvartn: Expression::stringFieldPath('variation'),
        ),
        pipeline: $embeddedPipeline,
        as: 'orders',
    );
}

Then, in your main Pipeline instance, call the lookupOrdersStage() function:

lookupOrdersStage($embeddedPipeline),

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

Stage::match(
    orders: Query::ne([])
),

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

Stage::unset('_id', 'description')

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

$cursor = $products->aggregate($pipeline);

Finally, run the following command in your shell to start your application:

php agg_tutorial.php

Interpret the aggregation results.

{
    "name": "Asus Laptop",
    "variation": "Standard Display",
    "category": "ELECTRONICS",
    "orders": [
        {
            "customer_id": "elise_smith@myemail.com",
            "orderdate": {
                "$date": {
                    "$numberLong": "1590827752000"
                }
            },
            "value": 431.43
        },
        {
            "customer_id": "jjones@tepidmail.com",
            "orderdate": {
                "$date": {
                    "$numberLong": "1608972946000"
                }
            },
            "value": 429.65
        }
    ]
}
{
    "name": "Morphy Richards Food Mixer",
    "variation": "Deluxe",
    "category": "KITCHENWARE",
    "orders": [
        {
            "customer_id": "oranieri@warmmail.com",
            "orderdate": {
                "$date": {
                    "$numberLong": "1577867137000"
                }
            },
            "value": 63.13
        }
    ]
}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

embedded_pl = [
    {
        "$match": {
            "$expr": {
                "$and": [
                    {"$eq": ["$product_name", "$$prdname"]},
                    {"$eq": ["$product_variation", "$$prdvartn"]},
                ]
            }
        }
    }
]

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

embedded_pl.append(
    {
        "$match": {
            "orderdate": {
                "$gte": datetime(2020, 1, 1, 0, 0, 0),
                "$lt": datetime(2021, 1, 1, 0, 0, 0),
            }
        }
    }
)

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

embedded_pl.append({"$unset": ["_id", "product_name", "product_variation"]})

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

pipeline.append(
    {
        "$lookup": {
            "from": "orders",
            "let": {"prdname": "$name", "prdvartn": "$variation"},
            "pipeline": embedded_pl,
            "as": "orders",
        }
    }
)

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

pipeline.append({"$match": {"orders": {"$ne": []}}})

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

pipeline.append({"$unset": ["_id", "description"]})

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

aggregation_result = products_coll.aggregate(pipeline)

Finally, run the following command in your shell to start your application:

python3 agg_tutorial.py

Interpret the aggregation results.

{'name': 'Asus Laptop', 'variation': 'Standard Display', 'category': 'ELECTRONICS', 'orders': [{'customer_id': 'elise_smith@myemail.com', 'orderdate': datetime.datetime(2020, 5, 30, 8, 35, 52), 'value': 431.43}, {'customer_id': 'jjones@tepidmail.com', 'orderdate': datetime.datetime(2020, 12, 26, 8, 55, 46), 'value': 429.65}]}
{'name': 'Morphy Richards Food Mixer', 'variation': 'Deluxe', 'category': 'KITCHENWARE', 'orders': [{'customer_id': 'oranieri@warmmail.com', 'orderdate': datetime.datetime(2020, 1, 1, 8, 25, 37), 'value': 63.13}]}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

{
  "$match": {
    "$expr": {
      "$and": [
        { "$eq": ["$product_name", "$$prdname"] },
        { "$eq": ["$product_variation", "$$prdvartn"] },
      ],
    },
  },
},

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

{
  "$match": {
    orderdate: {
      "$gte": DateTime.parse("2020-01-01T00:00:00Z"),
      "$lt": DateTime.parse("2021-01-01T00:00:00Z"),
    },
  },
},

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

{
  "$unset": ["_id", "product_name", "product_variation"],
},

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

{
  "$lookup": {
    from: "orders",
    let: {
      prdname: "$name",
      prdvartn: "$variation",
    },
    pipeline: embedded_pipeline,
    as: "orders",
  },
},

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

{
  "$match": {
    orders: { "$ne": [] },
  },
},

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

{
  "$unset": ["_id", "description"],
},

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

aggregation_result = products.aggregate(pipeline)

Finally, run the following command in your shell to start your application:

ruby agg_tutorial.rb

Interpret the aggregation results.

{"name"=>"Asus Laptop", "variation"=>"Standard Display", "category"=>"ELECTRONICS", "orders"=>[{"customer_id"=>"elise_smith@myemail.com", "orderdate"=>2020-05-30 08:35:52 UTC, "value"=>431.43}, {"customer_id"=>"jjones@tepidmail.com", "orderdate"=>2020-12-26 08:55:46 UTC, "value"=>429.65}]}
{"name"=>"Morphy Richards Food Mixer", "variation"=>"Deluxe", "category"=>"KITCHENWARE", "orders"=>[{"customer_id"=>"oranieri@warmmail.com", "orderdate"=>2020-01-01 08:25:37 UTC, "value"=>63.13}]}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

let mut embedded_pipeline = Vec::new();
embedded_pipeline.push(doc! {
    "$match": {
        "$expr": {
            "$and": [
                { "$eq": ["$product_name", "$$prdname"] },
                { "$eq": ["$product_variation", "$$prdvartn"] }
            ]
        }
    }
});

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

embedded_pipeline.push(doc! {
    "$match": {
        "order_date": {
            "$gte": DateTime::builder().year(2020).month(1).day(1).build().unwrap(),
            "$lt": DateTime::builder().year(2021).month(1).day(1).build().unwrap()
        }
    }
});

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

embedded_pipeline.push(doc! {
    "$unset": ["_id", "product_name", "product_variation"]
});

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

pipeline.push(doc! {
    "$lookup": {
        "from": "orders",
        "let": {
            "prdname": "$name",
            "prdvartn": "$variation"
        },
        "pipeline": embedded_pipeline,
        "as": "orders"
    }
});

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

pipeline.push(doc! {
    "$match": {
        "orders": { "$ne": [] }
    }
});

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

pipeline.push(doc! {
    "$unset": ["_id", "description"]
});

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

let mut cursor = products.aggregate(pipeline).await?;

Finally, run the following command in your shell to start your application:

cargo run

Interpret the aggregation results.

Document({"name": String("Asus Laptop"), "variation": String("Standard Display"), "category": String("ELECTRONICS"),
"orders": Array([Document({"customer_id": String("elise_smith@myemail.com"), "order_date": DateTime(2020-05-30 8:35:52.0 +00:00:00),
"value": Double(431.42999267578125)}), Document({"customer_id": String("jjones@tepidmail.com"), "order_date":
DateTime(2020-12-26 8:55:46.0 +00:00:00), "value": Double(429.6499938964844)})])})
Document({"name": String("Morphy Richards Food Mixer"), "variation": String("Deluxe"), "category": String("KITCHENWARE"),
"orders": Array([Document({"customer_id": String("oranieri@warmmail.com"), "order_date": DateTime(2020-01-01 8:25:37.0 +00:00:00),
"value": Double(63.130001068115234)})])})

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Add a lookup stage to link the collections and import fields.

Aggregates.filter(
  Filters.expr(
    Filters.and(
      Document("$eq" -> Seq("$product_name", "$$prdname")),
      Document("$eq" -> Seq("$product_variation", "$$prdvartn"))
    )
  )
),

Within the embedded pipeline, add another $match stage to match orders placed in 2020:

Aggregates.filter(
  Filters.and(
    Filters.gte("orderdate", dateFormat.parse("2020-01-01T00:00:00")),
    Filters.lt("orderdate", dateFormat.parse("2021-01-01T00:00:00"))
  )
),

Within the embedded pipeline, add an $unset stage to remove unneeded fields from the orders collection side of the join:

Aggregates.unset("_id", "product_name", "product_variation"),

After the embedded pipeline is completed, add the $lookup stage to the main aggregation pipeline. Configure this stage to store the processed lookup fields in an array field called orders:

Aggregates.lookup(
  "orders",
  Seq(
    Variable("prdname", "$name"),
    Variable("prdvartn", "$variation"),
  ),
  embeddedPipeline,
  "orders"
),

Add a match stage for products ordered in 2020.

Next, add a $match stage to only show products for which there is at least one order in 2020, based on the orders array calculated in the previous step:

Aggregates.filter(Filters.ne("orders", Seq())),

Add an unset stage to remove unneeded fields.

Finally, add an $unset stage. The $unset stage removes the _id and description fields from the result documents:

Aggregates.unset("_id", "description")

Run the aggregation pipeline.

Add the following code to the end of your application to perform the aggregation on the products collection:

products.aggregate(pipeline)
  .subscribe(
    (doc: Document) => println(doc.toJson()),
    (e: Throwable) => println(s"Error: $e"),
  )

Finally, run the application in your IDE.

Interpret the aggregation results.

{"name": "Asus Laptop", "variation": "Standard Display", "category": "ELECTRONICS", "orders": [{"customer_id": "elise_smith@myemail.com", "orderdate": {"$date": "2020-05-30T12:35:52Z"}, "value": 431.43}, {"customer_id": "jjones@tepidmail.com", "orderdate": {"$date": "2020-12-26T13:55:46Z"}, "value": 429.65}]}
{"name": "Morphy Richards Food Mixer", "variation": "Deluxe", "category": "KITCHENWARE", "orders": [{"customer_id": "oranieri@warmmail.com", "orderdate": {"$date": "2020-01-01T13:25:37Z"}, "value": 63.13}]}

The result documents contain details from documents in the orders collection and the products collection, joined by the product names and variations.

Back

One-to-One Join

Reference