9.28. 事件觸發函式
PostgreSQLprovides these helper functions to retrieve information from event triggers.
For more information about event triggers, seeChapter 39.
9.28.1. Capturing Changes at Command End
pg_event_trigger_ddl_commands
returns a list ofDDLcommands executed by each user action, when invoked in a function attached to addl_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; otherwiseNULL . 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 whosesql_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; otherwiseNULL . 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; otherwiseNULL . 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 withobject_type andaddress_args , can be used by thepg_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 foraddress_names above. |
Thepg_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 inTable 9.90provide information about a table for which atable_rewrite
event has just been called. If called in any other context, an error is raised.
Table 9.90. 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. |
Thepg_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();