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PL/Python: Add event trigger support

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Allow event triggers to be written in PL/Python.  It provides a TD
dictionary with some information about the event trigger.

Author: Euler Taveira <euler@eulerto.com>
Co-authored-by: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/03f03515-2068-4f5b-b357-8fb540883c38%40app.fastmail.com
This commit is contained in:
Peter Eisentraut
2025-08-21 09:15:55 +02:00
parent 6e09c960eb
commit 53eff471c6
7 changed files with 182 additions and 0 deletions
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doc/src/sgml/plpython.sgml
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@@ -662,6 +662,14 @@ $$ LANGUAGE plpython3u;
<secondary>in PL/Python</secondary>
</indexterm>
<para>
<application>PL/Python</application> can be used to define trigger
functions.
<productname>PostgreSQL</productname> requires that a function that is to
be called as a trigger must be declared as a function with no arguments and
a return type of <literal>trigger</literal>.
</para>
<para>
When a function is used as a trigger, the dictionary
<literal>TD</literal> contains trigger-related values:
@@ -769,6 +777,74 @@ $$ LANGUAGE plpython3u;
</para>
</sect1>
<sect1 id="plpython-event-trigger">
<title>Event Trigger Functions</title>
<indexterm zone="plpython-event-trigger">
<primary>event trigger</primary>
<secondary>in PL/Python</secondary>
</indexterm>
<para>
<application>PL/Python</application> can be used to define event triggers
(see also <xref linkend="event-triggers"/>).
<productname>PostgreSQL</productname> requires that a function that is to
be called as an event trigger must be declared as a function with no
arguments and a return type of <literal>event_trigger</literal>.
</para>
<para>
When a function is used as an event trigger, the dictionary
<literal>TD</literal> contains trigger-related values:
<variablelist>
<varlistentry>
<term><varname>TD["event"]</varname></term>
<listitem>
<para>
The event the trigger was fired for, as a string, for example
<literal>ddl_command_start</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>TD["tag"]</varname></term>
<listitem>
<para>
The command tag for which the trigger was fired, as a string, for
example <literal>DROP TABLE</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
<xref linkend="plpython-event-trigger-example"/> shows an example of an
event trigger function in <application>PL/Python</application>.
</para>
<example id="plpython-event-trigger-example">
<title>A <application>PL/Python</application> Event Trigger Function</title>
<para>
This example trigger simply raises a <literal>NOTICE</literal> message
each time a supported command is executed.
</para>
<programlisting>
CREATE OR REPLACE FUNCTION pysnitch() RETURNS event_trigger
LANGUAGE plpython3u
AS $$
plpy.notice("TD[event] => " + TD["event"] + " ; TD[tag] => " + TD["tag"]);
$$;
CREATE EVENT TRIGGER pysnitch ON ddl_command_start EXECUTE FUNCTION pysnitch();
</programlisting>
</example>
</sect1>
<sect1 id="plpython-database">
<title>Database Access</title>