Offer triggers on foreign tables.

This covers all the SQL-standard trigger types supported for regular
tables; it does not cover constraint triggers.  The approach for
acquiring the old row mirrors that for view INSTEAD OF triggers.  For
AFTER ROW triggers, we spool the foreign tuples to a tuplestore.

This changes the FDW API contract; when deciding which columns to
populate in the slot returned from data modification callbacks, writable
FDWs will need to check for AFTER ROW triggers in addition to checking
for a RETURNING clause.

In support of the feature addition, refactor the TriggerFlags bits and
the assembly of old tuples in ModifyTable.

Ronan Dunklau, reviewed by KaiGai Kohei; some additional hacking by me.

2 files changed, 81 insertions, 0 deletions

diff --git a/src/test/regress/expected/foreign_data.out b/src/test/regress/expected/foreign_data.out
index 60506e07b1c..c34c9b4df42 100644
--- a/src/test/regress/expected/foreign_data.out
+++ b/src/test/regress/expected/foreign_data.out
@@ -1158,6 +1158,43 @@ CREATE USER MAPPING FOR current_user SERVER s9;
 DROP SERVER s9 CASCADE;                                         -- ERROR
 ERROR:  must be owner of foreign server s9
 RESET ROLE;
+-- Triggers
+CREATE FUNCTION dummy_trigger() RETURNS TRIGGER AS $$
+  BEGIN
+    RETURN NULL;
+  END
+$$ language plpgsql;
+CREATE TRIGGER trigtest_before_stmt BEFORE INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH STATEMENT
+EXECUTE PROCEDURE dummy_trigger();
+CREATE TRIGGER trigtest_after_stmt AFTER INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH STATEMENT
+EXECUTE PROCEDURE dummy_trigger();
+CREATE TRIGGER trigtest_before_row BEFORE INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH ROW
+EXECUTE PROCEDURE dummy_trigger();
+CREATE TRIGGER trigtest_after_row AFTER INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH ROW
+EXECUTE PROCEDURE dummy_trigger();
+CREATE CONSTRAINT TRIGGER trigtest_constraint AFTER INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH ROW
+EXECUTE PROCEDURE dummy_trigger();
+ERROR:  "foreign_table_1" is a foreign table
+DETAIL:  Foreign tables cannot have constraint triggers.
+ALTER FOREIGN TABLE foreign_schema.foreign_table_1
+	DISABLE TRIGGER trigtest_before_stmt;
+ALTER FOREIGN TABLE foreign_schema.foreign_table_1
+	ENABLE TRIGGER trigtest_before_stmt;
+DROP TRIGGER trigtest_before_stmt ON foreign_schema.foreign_table_1;
+DROP TRIGGER trigtest_before_row ON foreign_schema.foreign_table_1;
+DROP TRIGGER trigtest_after_stmt ON foreign_schema.foreign_table_1;
+DROP TRIGGER trigtest_after_row ON foreign_schema.foreign_table_1;
+DROP FUNCTION dummy_trigger();
 -- DROP FOREIGN TABLE
 DROP FOREIGN TABLE no_table;                                    -- ERROR
 ERROR:  foreign table "no_table" does not exist
diff --git a/src/test/regress/sql/foreign_data.sql b/src/test/regress/sql/foreign_data.sql
index f819eb1b8eb..0f0869ee268 100644
--- a/src/test/regress/sql/foreign_data.sql
+++ b/src/test/regress/sql/foreign_data.sql
@@ -470,6 +470,50 @@ CREATE USER MAPPING FOR current_user SERVER s9;
 DROP SERVER s9 CASCADE;                                         -- ERROR
 RESET ROLE;
 
+-- Triggers
+CREATE FUNCTION dummy_trigger() RETURNS TRIGGER AS $$
+  BEGIN
+    RETURN NULL;
+  END
+$$ language plpgsql;
+
+CREATE TRIGGER trigtest_before_stmt BEFORE INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH STATEMENT
+EXECUTE PROCEDURE dummy_trigger();
+
+CREATE TRIGGER trigtest_after_stmt AFTER INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH STATEMENT
+EXECUTE PROCEDURE dummy_trigger();
+
+CREATE TRIGGER trigtest_before_row BEFORE INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH ROW
+EXECUTE PROCEDURE dummy_trigger();
+
+CREATE TRIGGER trigtest_after_row AFTER INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH ROW
+EXECUTE PROCEDURE dummy_trigger();
+
+CREATE CONSTRAINT TRIGGER trigtest_constraint AFTER INSERT OR UPDATE OR DELETE
+ON foreign_schema.foreign_table_1
+FOR EACH ROW
+EXECUTE PROCEDURE dummy_trigger();
+
+ALTER FOREIGN TABLE foreign_schema.foreign_table_1
+	DISABLE TRIGGER trigtest_before_stmt;
+ALTER FOREIGN TABLE foreign_schema.foreign_table_1
+	ENABLE TRIGGER trigtest_before_stmt;
+
+DROP TRIGGER trigtest_before_stmt ON foreign_schema.foreign_table_1;
+DROP TRIGGER trigtest_before_row ON foreign_schema.foreign_table_1;
+DROP TRIGGER trigtest_after_stmt ON foreign_schema.foreign_table_1;
+DROP TRIGGER trigtest_after_row ON foreign_schema.foreign_table_1;
+
+DROP FUNCTION dummy_trigger();
+
 -- DROP FOREIGN TABLE
 DROP FOREIGN TABLE no_table;                                    -- ERROR
 DROP FOREIGN TABLE IF EXISTS no_table;