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diff --git a/doc/src/sgml/html/event-trigger-example.html b/doc/src/sgml/html/event-trigger-example.html new file mode 100644 index 0000000..b6ca0b7 --- /dev/null +++ b/doc/src/sgml/html/event-trigger-example.html @@ -0,0 +1,78 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>40.4. A Complete Event Trigger Example</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="event-trigger-interface.html" title="40.3. Writing Event Trigger Functions in C" /><link rel="next" href="event-trigger-table-rewrite-example.html" title="40.5. A Table Rewrite Event Trigger Example" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">40.4. A Complete Event Trigger Example</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="event-trigger-interface.html" title="40.3. Writing Event Trigger Functions in C">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="event-triggers.html" title="Chapter 40. Event Triggers">Up</a></td><th width="60%" align="center">Chapter 40. Event Triggers</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="event-trigger-table-rewrite-example.html" title="40.5. A Table Rewrite Event Trigger Example">Next</a></td></tr></table><hr /></div><div class="sect1" id="EVENT-TRIGGER-EXAMPLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">40.4. A Complete Event Trigger Example <a href="#EVENT-TRIGGER-EXAMPLE" class="id_link">#</a></h2></div></div></div><p> + Here is a very simple example of an event trigger function written in C. + (Examples of triggers written in procedural languages can be found in + the documentation of the procedural languages.) + </p><p> + The function <code class="function">noddl</code> raises an exception each time it is called. + The event trigger definition associated the function with + the <code class="literal">ddl_command_start</code> event. The effect is that all DDL + commands (with the exceptions mentioned + in <a class="xref" href="event-trigger-definition.html" title="40.1. Overview of Event Trigger Behavior">Section 40.1</a>) are prevented from running. + </p><p> + This is the source code of the trigger function: +</p><pre class="programlisting"> +#include "postgres.h" +#include "commands/event_trigger.h" + + +PG_MODULE_MAGIC; + +PG_FUNCTION_INFO_V1(noddl); + +Datum +noddl(PG_FUNCTION_ARGS) +{ + EventTriggerData *trigdata; + + if (!CALLED_AS_EVENT_TRIGGER(fcinfo)) /* internal error */ + elog(ERROR, "not fired by event trigger manager"); + + trigdata = (EventTriggerData *) fcinfo->context; + + ereport(ERROR, + (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE), + errmsg("command \"%s\" denied", + GetCommandTagName(trigdata->tag)))); + + PG_RETURN_NULL(); +} +</pre><p> + </p><p> + After you have compiled the source code (see <a class="xref" href="xfunc-c.html#DFUNC" title="38.10.5. Compiling and Linking Dynamically-Loaded Functions">Section 38.10.5</a>), + declare the function and the triggers: +</p><pre class="programlisting"> +CREATE FUNCTION noddl() RETURNS event_trigger + AS 'noddl' LANGUAGE C; + +CREATE EVENT TRIGGER noddl ON ddl_command_start + EXECUTE FUNCTION noddl(); +</pre><p> + </p><p> + Now you can test the operation of the trigger: +</p><pre class="screen"> +=# \dy + List of event triggers + Name | Event | Owner | Enabled | Function | Tags +-------+-------------------+-------+---------+----------+------ + noddl | ddl_command_start | dim | enabled | noddl | +(1 row) + +=# CREATE TABLE foo(id serial); +ERROR: command "CREATE TABLE" denied +</pre><p> + </p><p> + In this situation, in order to be able to run some DDL commands when you + need to do so, you have to either drop the event trigger or disable it. It + can be convenient to disable the trigger for only the duration of a + transaction: +</p><pre class="programlisting"> +BEGIN; +ALTER EVENT TRIGGER noddl DISABLE; +CREATE TABLE foo (id serial); +ALTER EVENT TRIGGER noddl ENABLE; +COMMIT; +</pre><p> + (Recall that DDL commands on event triggers themselves are not affected by + event triggers.) + </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="event-trigger-interface.html" title="40.3. Writing Event Trigger Functions in C">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="event-triggers.html" title="Chapter 40. Event Triggers">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="event-trigger-table-rewrite-example.html" title="40.5. A Table Rewrite Event Trigger Example">Next</a></td></tr><tr><td width="40%" align="left" valign="top">40.3. Writing Event Trigger Functions in C </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 40.5. A Table Rewrite Event Trigger Example</td></tr></table></div></body></html>
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