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<sect1 id="functions-event-triggers">
<title>Event Trigger Functions</title>
<para>
<productname>PostgreSQL</productname> provides these helper functions
to retrieve information from event triggers.
</para>
<para>
For more information about event triggers,
see <xref linkend="event-triggers"/>.
</para>
<sect2 id="pg-event-trigger-ddl-command-end-functions">
<title>Capturing Changes at Command End</title>
<indexterm>
<primary>pg_event_trigger_ddl_commands</primary>
</indexterm>
<synopsis>
<function>pg_event_trigger_ddl_commands</function> () <returnvalue>setof record</returnvalue>
</synopsis>
<para>
<function>pg_event_trigger_ddl_commands</function> returns a list of
<acronym>DDL</acronym> commands executed by each user action,
when invoked in a function attached to a
<literal>ddl_command_end</literal> event trigger. If called in any other
context, an error is raised.
<function>pg_event_trigger_ddl_commands</function> 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:
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>classid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of catalog the object belongs in</entry>
</row>
<row>
<entry><literal>objid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of the object itself</entry>
</row>
<row>
<entry><literal>objsubid</literal></entry>
<entry><type>integer</type></entry>
<entry>Sub-object ID (e.g., attribute number for a column)</entry>
</row>
<row>
<entry><literal>command_tag</literal></entry>
<entry><type>text</type></entry>
<entry>Command tag</entry>
</row>
<row>
<entry><literal>object_type</literal></entry>
<entry><type>text</type></entry>
<entry>Type of the object</entry>
</row>
<row>
<entry><literal>schema_name</literal></entry>
<entry><type>text</type></entry>
<entry>
Name of the schema the object belongs in, if any; otherwise <literal>NULL</literal>.
No quoting is applied.
</entry>
</row>
<row>
<entry><literal>object_identity</literal></entry>
<entry><type>text</type></entry>
<entry>
Text rendering of the object identity, schema-qualified. Each
identifier included in the identity is quoted if necessary.
</entry>
</row>
<row>
<entry><literal>in_extension</literal></entry>
<entry><type>boolean</type></entry>
<entry>True if the command is part of an extension script</entry>
</row>
<row>
<entry><literal>command</literal></entry>
<entry><type>pg_ddl_command</type></entry>
<entry>
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.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect2>
<sect2 id="pg-event-trigger-sql-drop-functions">
<title>Processing Objects Dropped by a DDL Command</title>
<indexterm>
<primary>pg_event_trigger_dropped_objects</primary>
</indexterm>
<synopsis>
<function>pg_event_trigger_dropped_objects</function> () <returnvalue>setof record</returnvalue>
</synopsis>
<para>
<function>pg_event_trigger_dropped_objects</function> returns a list of all objects
dropped by the command in whose <literal>sql_drop</literal> event it is called.
If called in any other context, an error is raised.
This function returns the following columns:
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry>Name</entry>
<entry>Type</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>classid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of catalog the object belonged in</entry>
</row>
<row>
<entry><literal>objid</literal></entry>
<entry><type>oid</type></entry>
<entry>OID of the object itself</entry>
</row>
<row>
<entry><literal>objsubid</literal></entry>
<entry><type>integer</type></entry>
<entry>Sub-object ID (e.g., attribute number for a column)</entry>
</row>
<row>
<entry><literal>original</literal></entry>
<entry><type>boolean</type></entry>
<entry>True if this was one of the root object(s) of the deletion</entry>
</row>
<row>
<entry><literal>normal</literal></entry>
<entry><type>boolean</type></entry>
<entry>
True if there was a normal dependency relationship
in the dependency graph leading to this object
</entry>
</row>
<row>
<entry><literal>is_temporary</literal></entry>
<entry><type>boolean</type></entry>
<entry>
True if this was a temporary object
</entry>
</row>
<row>
<entry><literal>object_type</literal></entry>
<entry><type>text</type></entry>
<entry>Type of the object</entry>
</row>
<row>
<entry><literal>schema_name</literal></entry>
<entry><type>text</type></entry>
<entry>
Name of the schema the object belonged in, if any; otherwise <literal>NULL</literal>.
No quoting is applied.
</entry>
</row>
<row>
<entry><literal>object_name</literal></entry>
<entry><type>text</type></entry>
<entry>
Name of the object, if the combination of schema and name can be
used as a unique identifier for the object; otherwise <literal>NULL</literal>.
No quoting is applied, and name is never schema-qualified.
</entry>
</row>
<row>
<entry><literal>object_identity</literal></entry>
<entry><type>text</type></entry>
<entry>
Text rendering of the object identity, schema-qualified. Each
identifier included in the identity is quoted if necessary.
</entry>
</row>
<row>
<entry><literal>address_names</literal></entry>
<entry><type>text[]</type></entry>
<entry>
An array that, together with <literal>object_type</literal> and
<literal>address_args</literal>, can be used by
the <function>pg_get_object_address</function> function to
recreate the object address in a remote server containing an
identically named object of the same kind.
</entry>
</row>
<row>
<entry><literal>address_args</literal></entry>
<entry><type>text[]</type></entry>
<entry>
Complement for <literal>address_names</literal>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
<para>
The <function>pg_event_trigger_dropped_objects</function> function can be used
in an event trigger like this:
<programlisting>
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();
</programlisting>
</para>
</sect2>
<sect2 id="pg-event-trigger-table-rewrite-functions">
<title>Handling a Table Rewrite Event</title>
<para>
The functions shown in
<xref linkend="functions-event-trigger-table-rewrite"/>
provide information about a table for which a
<literal>table_rewrite</literal> event has just been called.
If called in any other context, an error is raised.
</para>
<table id="functions-event-trigger-table-rewrite">
<title>Table Rewrite Information Functions</title>
<tgroup cols="1">
<thead>
<row>
<entry role="func_table_entry"><para role="func_signature">
Function
</para>
<para>
Description
</para></entry>
</row>
</thead>
<tbody>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_event_trigger_table_rewrite_oid</primary>
</indexterm>
<function>pg_event_trigger_table_rewrite_oid</function> ()
<returnvalue>oid</returnvalue>
</para>
<para>
Returns the OID of the table about to be rewritten.
</para></entry>
</row>
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
<primary>pg_event_trigger_table_rewrite_reason</primary>
</indexterm>
<function>pg_event_trigger_table_rewrite_reason</function> ()
<returnvalue>integer</returnvalue>
</para>
<para>
Returns a code explaining the reason(s) for rewriting. The value is
a bitmap built from the following values: <literal>1</literal>
(the table has changed its persistence), <literal>2</literal>
(default value of a column has changed), <literal>4</literal>
(a column has a new data type) and <literal>8</literal>
(the table access method has changed).
</para></entry>
</row>
</tbody>
</tgroup>
</table>
<para>
These functions can be used in an event trigger like this:
<programlisting>
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();
</programlisting>
</para>
</sect2>
</sect1>
|
