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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!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>44.6. PL/Perl Triggers</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 V1.79.1" /><link rel="prev" href="plperl-trusted.html" title="44.5. Trusted and Untrusted PL/Perl" /><link rel="next" href="plperl-event-triggers.html" title="44.7. PL/Perl Event Triggers" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">44.6. PL/Perl Triggers</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plperl-trusted.html" title="44.5. Trusted and Untrusted PL/Perl">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plperl.html" title="Chapter 44. PL/Perl - Perl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 44. PL/Perl - Perl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plperl-event-triggers.html" title="44.7. PL/Perl Event Triggers">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PLPERL-TRIGGERS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">44.6. PL/Perl Triggers</h2></div></div></div><p>

  3.    PL/Perl can be used to write trigger functions.  In a trigger function,

  4.    the hash reference <code class="varname">$_TD</code> contains information about the

  5.    current trigger event. <code class="varname">$_TD</code> is a global variable,

  6.    which gets a separate local value for each invocation of the trigger.

  7.    The fields of the <code class="varname">$_TD</code> hash reference are:

  8. 

  9.    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">$_TD-&gt;{new}{foo}</code></span></dt><dd><p>

  10.        <code class="literal">NEW</code> value of column <code class="literal">foo</code>

  11.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{old}{foo}</code></span></dt><dd><p>

  12.        <code class="literal">OLD</code> value of column <code class="literal">foo</code>

  13.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{name}</code></span></dt><dd><p>

  14.        Name of the trigger being called

  15.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{event}</code></span></dt><dd><p>

  16.        Trigger event: <code class="literal">INSERT</code>, <code class="literal">UPDATE</code>,

  17.        <code class="literal">DELETE</code>, <code class="literal">TRUNCATE</code>, or <code class="literal">UNKNOWN</code>

  18.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{when}</code></span></dt><dd><p>

  19.        When the trigger was called: <code class="literal">BEFORE</code>,

  20.        <code class="literal">AFTER</code>, <code class="literal">INSTEAD OF</code>, or

  21.        <code class="literal">UNKNOWN</code>

  22.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{level}</code></span></dt><dd><p>

  23.        The trigger level: <code class="literal">ROW</code>, <code class="literal">STATEMENT</code>, or <code class="literal">UNKNOWN</code>

  24.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{relid}</code></span></dt><dd><p>

  25.        OID of the table on which the trigger fired

  26.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{table_name}</code></span></dt><dd><p>

  27.        Name of the table on which the trigger fired

  28.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{relname}</code></span></dt><dd><p>

  29.        Name of the table on which the trigger fired. This has been deprecated,

  30.        and could be removed in a future release.

  31.        Please use $_TD-&gt;{table_name} instead.

  32.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{table_schema}</code></span></dt><dd><p>

  33.        Name of the schema in which the table on which the trigger fired, is

  34.       </p></dd><dt><span class="term"><code class="literal">$_TD-&gt;{argc}</code></span></dt><dd><p>

  35.        Number of arguments of the trigger function

  36.       </p></dd><dt><span class="term"><code class="literal">@{$_TD-&gt;{args}}</code></span></dt><dd><p>

  37.        Arguments of the trigger function.  Does not exist if <code class="literal">$_TD-&gt;{argc}</code> is 0.

  38.       </p></dd></dl></div><p>

  39.   </p><p>

  40.    Row-level triggers can return one of the following:

  41. 

  42.    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">return;</code></span></dt><dd><p>

  43.        Execute the operation

  44.       </p></dd><dt><span class="term"><code class="literal">"SKIP"</code></span></dt><dd><p>

  45.        Don't execute the operation

  46.       </p></dd><dt><span class="term"><code class="literal">"MODIFY"</code></span></dt><dd><p>

  47.        Indicates that the <code class="literal">NEW</code> row was modified by

  48.        the trigger function

  49.       </p></dd></dl></div><p>

  50.   </p><p>

  51.    Here is an example of a trigger function, illustrating some of the

  52.    above:

  53. </p><pre class="programlisting">

  54. CREATE TABLE test (

  55.     i int,

  56.     v varchar

  57. );

  58. 

  59. CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$

  60.     if (($_TD-&gt;{new}{i} &gt;= 100) || ($_TD-&gt;{new}{i} &lt;= 0)) {

  61.         return "SKIP";    # skip INSERT/UPDATE command

  62.     } elsif ($_TD-&gt;{new}{v} ne "immortal") {

  63.         $_TD-&gt;{new}{v} .= "(modified by trigger)";

  64.         return "MODIFY";  # modify row and execute INSERT/UPDATE command

  65.     } else {

  66.         return;           # execute INSERT/UPDATE command

  67.     }

  68. $$ LANGUAGE plperl;

  69. 

  70. CREATE TRIGGER test_valid_id_trig

  71.     BEFORE INSERT OR UPDATE ON test

  72.     FOR EACH ROW EXECUTE FUNCTION valid_id();

  73. </pre><p>

  74.   </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plperl-trusted.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plperl.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plperl-event-triggers.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">44.5. Trusted and Untrusted PL/Perl </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 44.7. PL/Perl Event Triggers</td></tr></table></div></body></html>
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