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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 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 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 37.

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