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9.28. Event Trigger Functions

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

For more information about event triggers, see Chapter 37.

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 in the catalog
objsubid integer Object sub-id (e.g. attribute number for columns)
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 and every identifier present in the identity is quoted if necessary.
in_extension bool whether 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 the object had within the catalog
objsubid int32 Object sub-id (e.g. attribute number for columns)
original bool Flag used to identify the root object(s) of the deletion
normal bool Flag indicating that there's a normal dependency relationship in the dependency graph leading to this object
is_temporary bool Flag indicating that the object 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 and every identifier present 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() 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 above.

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();

9.28.3. Handling a Table Rewrite Event

The functions shown in Table 9-78 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 9-78. 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 PROCEDURE test_event_trigger_table_rewrite_oid();

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