学习笔记054——MyBatis Plus相关笔记

1、创建MyBatis Plus简单工程

对 MyBatis 的封装，自动完成 SQL 语句的执行，以及结果集的映射，提供了很多接口，开发者可以直接调用，直接拿到结果，不需要定义 SQL 以及结果集到 Java 的映射。

pom.xml文件导入依赖

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.3.1</version>
</dependency>

创建实体类

package com.htl.entity;

import lombok.Data;

@Data
public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
}

接口继承BaseMapper

package com.htl.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.htl.entity.User;

public interface UserMapper extends BaseMapper<User> {
}

创建启动类

package com.htl;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.htl.mapper")
public class Mp001Application {

    public static void main(String[] args) {
        SpringApplication.run(Mp001Application.class, args);
    }

}

配置yaml文件

spring:
  datasource:
    username: root
    password: 123456
    url: jdbc:mysql://localhost:3306/test12
    driver-class-name: com.mysql.cj.jdbc.Driver

启动测试

package com.htl;

import com.htl.entity.User;
import com.htl.mapper.UserMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

import java.util.List;

@SpringBootTest
class Mp001ApplicationTests {

    @Autowired
    private UserMapper userMapper;

    @Test
    void contextLoads() {
        List<User> list = this.userMapper.selectList(null);
        for (User user : list) {
            System.out.println(user);
        }
    }

}

如果实体类中的成员变量和数据表中的字段不一致，可以通过注解的形式进行映射解决。

package com.htl.entity;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.Data;

@Data
@TableName("user")
public class Account {
    @TableId("id")
    private Integer num;
    @TableField("password")
    private String name;
    @TableField("username")
    private String pwd;
    @TableField("age")
    private Integer score;
}

2、常用注解

@TableName 映射实体类到表名

@TableId 映射主键

type：

AUTO(0),		数据库ID自增
NONE(1),		没有设置
INPUT(2),		添加之前要手动set值
ASSIGN_ID(3),	MP分配，Number/String
ASSIGN_UUID(4)  MP分配，String

@TableField 映射其他字段

exist、select = false，实体类中有额外的字段，和数据表不一致

fill 自动填充，MP 自动给字段赋值，常用于时间类型的数据

@TableField(value = "create_time",fill = FieldFill.INSERT)
private Date createTime;
@TableField(value = "update_time",fill = FieldFill.INSERT_UPDATE)
private Date updateTime;

配置处理器

package com.htl.handler;

import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
import org.apache.ibatis.reflection.MetaObject;
import org.springframework.stereotype.Component;

import java.util.Date;

@Component
public class DateHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
        this.setFieldValByName("createTime", new Date(),metaObject);
        this.setFieldValByName("updateTime", new Date(),metaObject);
    }

    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("updateTime", new Date(),metaObject);
    }
}

3、MyBatis Plus 代码自动生成

MyBatis 自动生成：根据数据表，自动生成实体类、Mapper 接口、Mapper.xml

MP 在此基础上，还可以自动生成 Controller、Service

1、pom.xml

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.3.1</version>
</dependency>

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-generator</artifactId>
    <version>3.3.2</version>
</dependency>

<dependency>
    <groupId>org.apache.velocity</groupId>
    <artifactId>velocity</artifactId>
    <version>1.7</version>
</dependency>

2、启动类

package com.htl;

import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.generator.AutoGenerator;
import com.baomidou.mybatisplus.generator.config.DataSourceConfig;
import com.baomidou.mybatisplus.generator.config.GlobalConfig;
import com.baomidou.mybatisplus.generator.config.PackageConfig;
import com.baomidou.mybatisplus.generator.config.StrategyConfig;
import com.baomidou.mybatisplus.generator.config.po.TableFill;
import com.baomidou.mybatisplus.generator.config.rules.NamingStrategy;

import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        //创建对象
        AutoGenerator autoGenerator = new AutoGenerator();
        //数据源
        DataSourceConfig dataSourceConfig = new DataSourceConfig();
        dataSourceConfig.setDbType(DbType.MYSQL);
        dataSourceConfig.setDriverName("com.mysql.cj.jdbc.Driver");
        dataSourceConfig.setUrl("jdbc:mysql://localhost:3306/mybatis_plus_note");
        dataSourceConfig.setUsername("root");
        dataSourceConfig.setPassword("password");
        autoGenerator.setDataSource(dataSourceConfig);
        //全局配置
        GlobalConfig globalConfig = new GlobalConfig();
        globalConfig.setOutputDir(System.getProperty("user.dir")+"/mp_generator001/src/main/java");
        globalConfig.setAuthor("作者名");
        globalConfig.setOpen(false);
        //去掉Service的I
        globalConfig.setServiceName("%sService");
        autoGenerator.setGlobalConfig(globalConfig);
        //包配置
        PackageConfig packageConfig = new PackageConfig();
        packageConfig.setParent("com.htl");
        packageConfig.setEntity("entity");
        packageConfig.setMapper("mapper");
        packageConfig.setService("service");
        packageConfig.setServiceImpl("service.impl");
        packageConfig.setController("controller");
        autoGenerator.setPackageInfo(packageConfig);
        //策略配置
        StrategyConfig strategyConfig = new StrategyConfig();
        strategyConfig.setInclude("user"); // 选择对应的表
        strategyConfig.setNaming(NamingStrategy.underline_to_camel);// 下划线转驼峰 （针对表名）
        strategyConfig.setColumnNaming(NamingStrategy.underline_to_camel);// 下划线转驼峰（针对字段名）
        strategyConfig.setEntityLombokModel(true);// 添加Lombok注解
        TableFill tableFill = new TableFill("create_time", FieldFill.INSERT);
        TableFill tableFill2 = new TableFill("update_time", FieldFill.INSERT_UPDATE);
        List<TableFill> list = Arrays.asList(tableFill,tableFill2);
        strategyConfig.setTableFillList(list);
        autoGenerator.setStrategy(strategyConfig);
        //启动
        autoGenerator.execute();
    }
}