9.28. 事件觸發函式

PostgreSQL provides these helper functions to retrieve information from event triggers.

For more information about event triggers, see Chapter 39.

9.28.1. Capturing Changes at Command End

pg_event_trigger_ddl_commands returns a list of DDL commands executed by each user action, when invoked in a function attached to a ddl_command_end event trigger. If called in any other context, an error is raised. pg_event_trigger_ddl_commands returns one row for each base command executed; some commands that are a single SQL sentence may return more than one row. This function returns the following columns:

Name	Type	Description
classid	oid	OID of catalog the object belongs in
objid	oid	OID of the object itself
objsubid	integer	Sub-object ID (e.g. attribute number for a column)
command_tag	text	Command tag
object_type	text	Type of the object
schema_name	text	Name of the schema the object belongs in, if any; otherwise NULL. No quoting is applied.
object_identity	text	Text rendering of the object identity, schema-qualified. Each identifier included in the identity is quoted if necessary.
in_extension	bool	True if the command is part of an extension script
command	pg_ddl_command	A complete representation of the command, in internal format. This cannot be output directly, but it can be passed to other functions to obtain different pieces of information about the command.

9.28.2. Processing Objects Dropped by a DDL Command

pg_event_trigger_dropped_objects returns a list of all objects dropped by the command in whose sql_drop event it is called. If called in any other context, pg_event_trigger_dropped_objects raises an error. pg_event_trigger_dropped_objects returns the following columns:

Name	Type	Description
classid	oid	OID of catalog the object belonged in
objid	oid	OID of the object itself
objsubid	integer	Sub-object ID (e.g. attribute number for a column)
original	bool	True if this was one of the root object(s) of the deletion
normal	bool	True if there was a normal dependency relationship in the dependency graph leading to this object
is_temporary	bool	True if this was a temporary object
object_type	text	Type of the object
schema_name	text	Name of the schema the object belonged in, if any; otherwise NULL. No quoting is applied.
object_name	text	Name of the object, if the combination of schema and name can be used as a unique identifier for the object; otherwise NULL. No quoting is applied, and name is never schema-qualified.
object_identity	text	Text rendering of the object identity, schema-qualified. Each identifier included in the identity is quoted if necessary.
address_names	text[]	An array that, together with object_type and address_args, can be used by the pg_get_object_address() function to recreate the object address in a remote server containing an identically named object of the same kind
address_args	text[]	Complement for address_names

The pg_event_trigger_dropped_objects function can be used in an event trigger like this:

CREATE FUNCTION test_event_trigger_for_drops()
        RETURNS event_trigger LANGUAGE plpgsql AS $$
DECLARE
    obj record;
BEGIN
    FOR obj IN SELECT * FROM pg_event_trigger_dropped_objects()
    LOOP
        RAISE NOTICE '% dropped object: % %.% %',
                     tg_tag,
                     obj.object_type,
                     obj.schema_name,
                     obj.object_name,
                     obj.object_identity;
    END LOOP;
END
$$;
CREATE EVENT TRIGGER test_event_trigger_for_drops
   ON sql_drop
   EXECUTE FUNCTION test_event_trigger_for_drops();

9.28.3. Handling a Table Rewrite Event

The functions shown in Table 9.96 provide information about a table for which a table_rewrite event has just been called. If called in any other context, an error is raised.

Table 9.96. Table Rewrite Information

Name	Return Type	Description
pg_event_trigger_table_rewrite_oid()	Oid	The OID of the table about to be rewritten.
pg_event_trigger_table_rewrite_reason()	int	The reason code(s) explaining the reason for rewriting. The exact meaning of the codes is release dependent.

The pg_event_trigger_table_rewrite_oid function can be used in an event trigger like this:

CREATE FUNCTION test_event_trigger_table_rewrite_oid()
 RETURNS event_trigger
 LANGUAGE plpgsql AS
$$
BEGIN
  RAISE NOTICE 'rewriting table % for reason %',
                pg_event_trigger_table_rewrite_oid()::regclass,
                pg_event_trigger_table_rewrite_reason();
END;
$$;

CREATE EVENT TRIGGER test_table_rewrite_oid
                  ON table_rewrite
   EXECUTE FUNCTION test_event_trigger_table_rewrite_oid();