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<!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>F.41. spi — Server Programming Interface features/examples</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="sepgsql.html" title="F.40. sepgsql — SELinux-, label-based mandatory access control (MAC) security module" /><link rel="next" href="sslinfo.html" title="F.42. sslinfo — obtain client SSL information" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.41. spi — Server Programming Interface features/examples</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sepgsql.html" title="F.40. sepgsql — SELinux-, label-based mandatory access control (MAC) security module">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules and Extensions">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules and Extensions</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sslinfo.html" title="F.42. sslinfo — obtain client SSL information">Next</a></td></tr></table><hr /></div><div class="sect1" id="CONTRIB-SPI"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.41. spi — Server Programming Interface features/examples <a href="#CONTRIB-SPI" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="contrib-spi.html#CONTRIB-SPI-REFINT">F.41.1. refint — Functions for Implementing Referential Integrity</a></span></dt><dt><span class="sect2"><a href="contrib-spi.html#CONTRIB-SPI-AUTOINC">F.41.2. autoinc — Functions for Autoincrementing Fields</a></span></dt><dt><span class="sect2"><a href="contrib-spi.html#CONTRIB-SPI-INSERT-USERNAME">F.41.3. insert_username — Functions for Tracking Who Changed a Table</a></span></dt><dt><span class="sect2"><a href="contrib-spi.html#CONTRIB-SPI-MODDATETIME">F.41.4. moddatetime — Functions for Tracking Last Modification Time</a></span></dt></dl></div><a id="id-1.11.7.51.2" class="indexterm"></a><p>
The <span class="application">spi</span> module provides several workable examples
of using the <a class="link" href="spi.html" title="Chapter 47. Server Programming Interface">Server Programming Interface</a>
(<acronym class="acronym">SPI</acronym>) and triggers. While these functions are of
some value in
their own right, they are even more useful as examples to modify for
your own purposes. The functions are general enough to be used
with any table, but you have to specify table and field names (as described
below) while creating a trigger.
</p><p>
Each of the groups of functions described below is provided as a
separately-installable extension.
</p><div class="sect2" id="CONTRIB-SPI-REFINT"><div class="titlepage"><div><div><h3 class="title">F.41.1. refint — Functions for Implementing Referential Integrity <a href="#CONTRIB-SPI-REFINT" class="id_link">#</a></h3></div></div></div><p>
<code class="function">check_primary_key()</code> and
<code class="function">check_foreign_key()</code> are used to check foreign key constraints.
(This functionality is long since superseded by the built-in foreign
key mechanism, of course, but the module is still useful as an example.)
</p><p>
<code class="function">check_primary_key()</code> checks the referencing table.
To use, create a <code class="literal">BEFORE INSERT OR UPDATE</code> trigger using this
function on a table referencing another table. Specify as the trigger
arguments: the referencing table's column name(s) which form the foreign
key, the referenced table name, and the column names in the referenced table
which form the primary/unique key. To handle multiple foreign
keys, create a trigger for each reference.
</p><p>
<code class="function">check_foreign_key()</code> checks the referenced table.
To use, create a <code class="literal">BEFORE DELETE OR UPDATE</code> trigger using this
function on a table referenced by other table(s). Specify as the trigger
arguments: the number of referencing tables for which the function has to
perform checking, the action if a referencing key is found
(<code class="literal">cascade</code> — to delete the referencing row,
<code class="literal">restrict</code> — to abort transaction if referencing keys
exist, <code class="literal">setnull</code> — to set referencing key fields to null),
the triggered table's column names which form the primary/unique key, then
the referencing table name and column names (repeated for as many
referencing tables as were specified by first argument). Note that the
primary/unique key columns should be marked NOT NULL and should have a
unique index.
</p><p>
There are examples in <code class="filename">refint.example</code>.
</p></div><div class="sect2" id="CONTRIB-SPI-AUTOINC"><div class="titlepage"><div><div><h3 class="title">F.41.2. autoinc — Functions for Autoincrementing Fields <a href="#CONTRIB-SPI-AUTOINC" class="id_link">#</a></h3></div></div></div><p>
<code class="function">autoinc()</code> is a trigger that stores the next value of
a sequence into an integer field. This has some overlap with the
built-in <span class="quote">“<span class="quote">serial column</span>”</span> feature, but it is not the same:
<code class="function">autoinc()</code> will override attempts to substitute a
different field value during inserts, and optionally it can be
used to increment the field during updates, too.
</p><p>
To use, create a <code class="literal">BEFORE INSERT</code> (or optionally <code class="literal">BEFORE
INSERT OR UPDATE</code>) trigger using this function. Specify two
trigger arguments: the name of the integer column to be modified,
and the name of the sequence object that will supply values.
(Actually, you can specify any number of pairs of such names, if
you'd like to update more than one autoincrementing column.)
</p><p>
There is an example in <code class="filename">autoinc.example</code>.
</p></div><div class="sect2" id="CONTRIB-SPI-INSERT-USERNAME"><div class="titlepage"><div><div><h3 class="title">F.41.3. insert_username — Functions for Tracking Who Changed a Table <a href="#CONTRIB-SPI-INSERT-USERNAME" class="id_link">#</a></h3></div></div></div><p>
<code class="function">insert_username()</code> is a trigger that stores the current
user's name into a text field. This can be useful for tracking
who last modified a particular row within a table.
</p><p>
To use, create a <code class="literal">BEFORE INSERT</code> and/or <code class="literal">UPDATE</code>
trigger using this function. Specify a single trigger
argument: the name of the text column to be modified.
</p><p>
There is an example in <code class="filename">insert_username.example</code>.
</p></div><div class="sect2" id="CONTRIB-SPI-MODDATETIME"><div class="titlepage"><div><div><h3 class="title">F.41.4. moddatetime — Functions for Tracking Last Modification Time <a href="#CONTRIB-SPI-MODDATETIME" class="id_link">#</a></h3></div></div></div><p>
<code class="function">moddatetime()</code> is a trigger that stores the current
time into a <code class="type">timestamp</code> field. This can be useful for tracking
the last modification time of a particular row within a table.
</p><p>
To use, create a <code class="literal">BEFORE UPDATE</code>
trigger using this function. Specify a single trigger
argument: the name of the column to be modified.
The column must be of type <code class="type">timestamp</code> or <code class="type">timestamp with
time zone</code>.
</p><p>
There is an example in <code class="filename">moddatetime.example</code>.
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