9.29. Event Trigger Functions

9.29. Event Trigger Functions
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9.29.1. Capturing Changes at Command End
9.29.2. Processing Objects Dropped by a DDL Command
9.29.3. Handling a Table Rewrite Event

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

+ For more information about event triggers, + see Chapter 40. +

9.29.1. Capturing Changes at Command End

+pg_event_trigger_ddl_commands () → setof record
+

+ 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`	`boolean`	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. +

9.29.2. Processing Objects Dropped by a DDL Command

+pg_event_trigger_dropped_objects () → setof record
+

+ 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, an error is raised. + This function 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`	`boolean`	True if this was one of the root object(s) of the deletion
`normal`	`boolean`	+ True if there was a normal dependency relationship + in the dependency graph leading to this object +
`is_temporary`	`boolean`	+ 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 FUNCTION test_event_trigger_for_drops();
+

9.29.3. Handling a Table Rewrite Event

+ The functions shown in + Table 9.102 + 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 9.102. Table Rewrite Information Functions

+ Function + + + Description +
+ + `pg_event_trigger_table_rewrite_oid` () + → `oid` + + + Returns the OID of the table about to be rewritten. +
+ + `pg_event_trigger_table_rewrite_reason` () + → `integer` + + + Returns a code explaining the reason(s) for rewriting. The exact + meaning of the codes is release dependent. +

+ Function +

+ Description +

+ + pg_event_trigger_table_rewrite_oid () + → oid +

+ Returns the OID of the table about to be rewritten. +

+ + pg_event_trigger_table_rewrite_reason () + → integer +

+ Returns a code explaining the reason(s) for rewriting. The exact + meaning of the codes is release dependent. +

+ These functions 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 FUNCTION test_event_trigger_table_rewrite_oid();
+

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