Postgres-XC 1.2 Documentation
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9.28. Event Trigger Functions

Currently PostgreSQL provides one built-in event trigger helper function, pg_event_trigger_dropped_objects.

pg_event_trigger_dropped_objects returns a list of all object 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 the object had within the catalog
`objsubid`	`int32`	Object sub-id (e.g. attribute number for columns)
`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 an 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 and every identifier present in the identity is quoted if necessary.

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 PROCEDURE test_event_trigger_for_drops();

For more information about event triggers, see Chapter 36.