PostgreSQL provides these helper functions to retrieve information from event triggers.
For more information about event triggers, see Chapter 39.
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. |
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 PROCEDURE test_event_trigger_for_drops();The functions shown in Table 9.90 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 9.90. Table Rewrite information
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();