PostgreSQL provides these helper functions to retrieve information from event triggers.
For more information about event triggers, see Chapter 38.
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 9-88 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 9-88. 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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