如何在 Postgres 中自动创建对 CREATE 的评论？

Question

我想创建一个触发器，一旦在模式中创建了 table，它就会被触发。此触发器应向新创建的 table 添加注释，例如：

CREATE TRIGGER my_trigger 
   AFTER CREATE ON my_schema
   EXECUTE PROCEDURE add_comment;

与 add_comment 一起做 somthibg：

...
BEGIN
   EXECUTE '
      COMMENT ON TABLE ' || new_table || ' IS ''Created by ' || CURRENT_USER || ' on ' || CURRENT_TIME ''';
   ';

但是，我似乎只能在 table 级别添加触发器。我怎样才能在纯 Postgres 中向新创建的 table 添加评论？

Answer 1

您需要 EVENT TRIGGER.

首先创建一个函数：

CREATE OR REPLACE FUNCTION trg_create_table_comment() RETURNS event_trigger
LANGUAGE plpgsql AS $$
DECLARE obj record;    
BEGIN
  SELECT * FROM pg_event_trigger_ddl_commands() INTO obj;
  EXECUTE 'COMMENT ON TABLE ' || obj.object_identity || ' IS ''Created by ' || SESSION_USER || ' on ' || NOW() || '''';
END;
$$;

然后将其附加到 EVENT TRIGGER:

CREATE EVENT TRIGGER trg_create_table ON ddl_command_end
WHEN TAG IN ('CREATE TABLE','CREATE TABLE AS')
EXECUTE PROCEDURE trg_create_table_comment();

创建 table 后将被触发：

CREATE TABLE foo (id int);

SELECT schemaname,tablename,tableowner,description
FROM pg_tables t
LEFT JOIN pg_description d ON d.objoid = t.tablename::regclass::oid
WHERE tablename = 'foo';
    
 schemaname | tablename | tableowner |                    description                    
------------+-----------+------------+---------------------------------------------------
 public     | foo       | jones      | Created by jones on 2021-04-10 20:22:22.174874+02

如何在 Postgres 中自动创建对 CREATE 的评论？

How to automatically create a comment on CREATE in Postgres?

sql

postgresql

triggers

plpgsql

postgresql-10