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PL/Python: Add event trigger support
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
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‎doc/src/sgml/plpython.sgml

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@@ -662,6 +662,14 @@ $$ LANGUAGE plpython3u;
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<secondary>in PL/Python</secondary>
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</indexterm>
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<para>
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<application>PL/Python</application> can be used to define trigger
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functions.
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<productname>PostgreSQL</productname> requires that a function that is to
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be called as a trigger must be declared as a function with no arguments and
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a return type of <literal>trigger</literal>.
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</para>
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<para>
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When a function is used as a trigger, the dictionary
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<literal>TD</literal> contains trigger-related values:
@@ -769,6 +777,74 @@ $$ LANGUAGE plpython3u;
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</para>
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</sect1>
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<sect1 id="plpython-event-trigger">
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<title>Event Trigger Functions</title>
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<indexterm zone="plpython-event-trigger">
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<primary>event trigger</primary>
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<secondary>in PL/Python</secondary>
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</indexterm>
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<para>
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<application>PL/Python</application> can be used to define event triggers
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(see also <xref linkend="event-triggers"/>).
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<productname>PostgreSQL</productname> requires that a function that is to
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be called as an event trigger must be declared as a function with no
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arguments and a return type of <literal>event_trigger</literal>.
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</para>
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<para>
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When a function is used as an event trigger, the dictionary
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<literal>TD</literal> contains trigger-related values:
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<variablelist>
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<varlistentry>
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<term><varname>TD["event"]</varname></term>
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<listitem>
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<para>
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The event the trigger was fired for, as a string, for example
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<literal>ddl_command_start</literal>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TD["tag"]</varname></term>
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<listitem>
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<para>
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The command tag for which the trigger was fired, as a string, for
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example <literal>DROP TABLE</literal>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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<xref linkend="plpython-event-trigger-example"/> shows an example of an
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event trigger function in <application>PL/Python</application>.
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</para>
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<example id="plpython-event-trigger-example">
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<title>A <application>PL/Python</application> Event Trigger Function</title>
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<para>
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This example trigger simply raises a <literal>NOTICE</literal> message
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each time a supported command is executed.
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</para>
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<programlisting>
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CREATE OR REPLACE FUNCTION pysnitch() RETURNS event_trigger
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LANGUAGE plpython3u
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AS $$
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plpy.notice("TD[event] => " + TD["event"] + " ; TD[tag] => " + TD["tag"]);
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$$;
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CREATE EVENT TRIGGER pysnitch ON ddl_command_start EXECUTE FUNCTION pysnitch();
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</programlisting>
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</example>
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</sect1>
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<sect1 id="plpython-database">
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<title>Database Access</title>
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‎src/pl/plpython/expected/plpython_trigger.out

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@@ -646,3 +646,30 @@ SELECT * FROM recursive_trigger_test;
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1 | 2
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(2 rows)
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-- event triggers
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CREATE OR REPLACE FUNCTION pysnitch() RETURNS event_trigger
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LANGUAGE plpython3u
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AS $$
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plpy.notice("TD[event] => " + TD["event"] + " ; TD[tag] => " + TD["tag"]);
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$$;
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CREATE EVENT TRIGGER python_a_snitch ON ddl_command_start
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EXECUTE PROCEDURE pysnitch();
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CREATE EVENT TRIGGER python_b_snitch ON ddl_command_end
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EXECUTE PROCEDURE pysnitch();
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CREATE OR REPLACE FUNCTION foobar() RETURNS int LANGUAGE sql AS $$SELECT 1;$$;
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NOTICE: TD[event] => ddl_command_start ; TD[tag] => CREATE FUNCTION
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NOTICE: TD[event] => ddl_command_end ; TD[tag] => CREATE FUNCTION
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ALTER FUNCTION foobar() COST 77;
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NOTICE: TD[event] => ddl_command_start ; TD[tag] => ALTER FUNCTION
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NOTICE: TD[event] => ddl_command_end ; TD[tag] => ALTER FUNCTION
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DROP FUNCTION foobar();
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NOTICE: TD[event] => ddl_command_start ; TD[tag] => DROP FUNCTION
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NOTICE: TD[event] => ddl_command_end ; TD[tag] => DROP FUNCTION
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CREATE TABLE foo();
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NOTICE: TD[event] => ddl_command_start ; TD[tag] => CREATE TABLE
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NOTICE: TD[event] => ddl_command_end ; TD[tag] => CREATE TABLE
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DROP TABLE foo;
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NOTICE: TD[event] => ddl_command_start ; TD[tag] => DROP TABLE
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NOTICE: TD[event] => ddl_command_end ; TD[tag] => DROP TABLE
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DROP EVENT TRIGGER python_a_snitch;
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DROP EVENT TRIGGER python_b_snitch;

‎src/pl/plpython/plpy_exec.c

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@@ -9,6 +9,7 @@
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#include "access/htup_details.h"
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#include "access/xact.h"
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#include "catalog/pg_type.h"
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#include "commands/event_trigger.h"
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#include "commands/trigger.h"
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#include "executor/spi.h"
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#include "funcapi.h"
@@ -427,6 +428,47 @@ PLy_exec_trigger(FunctionCallInfo fcinfo, PLyProcedure *proc)
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return rv;
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}
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/*
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* event trigger subhandler
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*/
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void
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PLy_exec_event_trigger(FunctionCallInfo fcinfo, PLyProcedure *proc)
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{
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EventTriggerData *tdata;
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PyObject *volatile pltdata = NULL;
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Assert(CALLED_AS_EVENT_TRIGGER(fcinfo));
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tdata = (EventTriggerData *) fcinfo->context;
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PG_TRY();
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{
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PyObject *pltevent,
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*plttag;
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pltdata = PyDict_New();
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if (!pltdata)
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PLy_elog(ERROR, NULL);
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pltevent = PLyUnicode_FromString(tdata->event);
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PyDict_SetItemString(pltdata, "event", pltevent);
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Py_DECREF(pltevent);
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plttag = PLyUnicode_FromString(GetCommandTagName(tdata->tag));
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PyDict_SetItemString(pltdata, "tag", plttag);
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Py_DECREF(plttag);
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PLy_procedure_call(proc, "TD", pltdata);
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if (SPI_finish() != SPI_OK_FINISH)
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elog(ERROR, "SPI_finish() failed");
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}
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PG_FINALLY();
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{
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Py_XDECREF(pltdata);
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}
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PG_END_TRY();
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}
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/* helper functions for Python code execution */
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static PyObject *

‎src/pl/plpython/plpy_exec.h

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@@ -9,5 +9,6 @@
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extern Datum PLy_exec_function(FunctionCallInfo fcinfo, PLyProcedure *proc);
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extern HeapTuple PLy_exec_trigger(FunctionCallInfo fcinfo, PLyProcedure *proc);
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extern void PLy_exec_event_trigger(FunctionCallInfo fcinfo, PLyProcedure *proc);
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#endif /* PLPY_EXEC_H */

‎src/pl/plpython/plpy_main.c

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@@ -9,6 +9,7 @@
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#include "access/htup_details.h"
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#include "catalog/pg_proc.h"
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#include "catalog/pg_type.h"
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#include "commands/event_trigger.h"
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#include "commands/trigger.h"
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#include "executor/spi.h"
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#include "miscadmin.h"
@@ -240,6 +241,13 @@ plpython3_call_handler(PG_FUNCTION_ARGS)
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trv = PLy_exec_trigger(fcinfo, proc);
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retval = PointerGetDatum(trv);
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}
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else if (CALLED_AS_EVENT_TRIGGER(fcinfo))
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{
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proc = PLy_procedure_get(funcoid, InvalidOid, PLPY_EVENT_TRIGGER);
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exec_ctx->curr_proc = proc;
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PLy_exec_event_trigger(fcinfo, proc);
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retval = (Datum) 0;
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}
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else
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{
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proc = PLy_procedure_get(funcoid, InvalidOid, PLPY_NOT_TRIGGER);
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case TRIGGEROID:
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ret = PLPY_TRIGGER;
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break;
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case EVENT_TRIGGEROID:
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ret = PLPY_EVENT_TRIGGER;
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break;
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default:
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ret = PLPY_NOT_TRIGGER;
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break;

‎src/pl/plpython/plpy_procedure.h

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@@ -17,6 +17,7 @@ extern void init_procedure_caches(void);
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typedef enum PLyTrigType
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{
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PLPY_TRIGGER,
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PLPY_EVENT_TRIGGER,
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PLPY_NOT_TRIGGER,
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} PLyTrigType;
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‎src/pl/plpython/sql/plpython_trigger.sql

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@@ -492,3 +492,27 @@ CREATE TRIGGER recursive_trigger_trig
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INSERT INTO recursive_trigger_test VALUES (0, 0);
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UPDATE recursive_trigger_test SET a = 11 WHERE b = 0;
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SELECT * FROM recursive_trigger_test;
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-- event triggers
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CREATE OR REPLACE FUNCTION pysnitch() RETURNS event_trigger
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LANGUAGE plpython3u
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AS $$
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plpy.notice("TD[event] => " + TD["event"] + " ; TD[tag] => " + TD["tag"]);
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$$;
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CREATE EVENT TRIGGER python_a_snitch ON ddl_command_start
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EXECUTE PROCEDURE pysnitch();
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CREATE EVENT TRIGGER python_b_snitch ON ddl_command_end
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EXECUTE PROCEDURE pysnitch();
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CREATE OR REPLACE FUNCTION foobar() RETURNS int LANGUAGE sql AS $$SELECT 1;$$;
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ALTER FUNCTION foobar() COST 77;
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DROP FUNCTION foobar();
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CREATE TABLE foo();
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DROP TABLE foo;
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DROP EVENT TRIGGER python_a_snitch;
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DROP EVENT TRIGGER python_b_snitch;

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