Adding upstream version 15.5.upstream/15.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+<!-- doc/src/sgml/contrib-spi.sgml -->
+
+<sect1 id="contrib-spi" xreflabel="spi">
+ <title>spi</title>
+
+ <indexterm zone="contrib-spi">
+  <primary>SPI</primary>
+  <secondary>examples</secondary>
+ </indexterm>
+
+ <para>
+  The <application>spi</application> module provides several workable examples
+  of using the <link linkend="spi">Server Programming Interface</link>
+  (<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.
+ </para>
+
+ <para>
+  Each of the groups of functions described below is provided as a
+  separately-installable extension.
+ </para>
+
+ <sect2>
+  <title>refint &mdash; Functions for Implementing Referential Integrity</title>
+
+  <para>
+   <function>check_primary_key()</function> and
+   <function>check_foreign_key()</function> 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+   (This functionality is long since superseded by the built-in foreign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.)
+  </para>
+
+  <para>
+   <function>check_primary_key()</function> checks the referencing table.
+   To use, create a <literal>BEFORE INSERT OR UPDATE</literal> 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.
+  </para>
+
+  <para>
+   <function>check_foreign_key()</function> checks the referenced table.
+   To use, create a <literal>BEFORE DELETE OR UPDATE</literal> 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
+   (<literal>cascade</literal> &mdash; to delete the referencing row,
+   <literal>restrict</literal> &mdash; to abort transaction if referencing keys
+   exist, <literal>setnull</literal> &mdash; 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.
+  </para>
+
+  <para>
+   There are examples in <filename>refint.example</filename>.
+  </para>
+ </sect2>
+
+ <sect2>
+  <title>autoinc &mdash; Functions for Autoincrementing Fields</title>
+
+  <para>
+   <function>autoinc()</function> is a trigger that stores the next value of
+   a sequence into an integer field.  This has some overlap with the
+   built-in <quote>serial column</quote> feature, but it is not the same:
+   <function>autoinc()</function> will override attempts to substitute a
+   different field value during inserts, and optionally it can be
+   used to increment the field during updates, too.
+  </para>
+
+  <para>
+   To use, create a <literal>BEFORE INSERT</literal> (or optionally <literal>BEFORE
+   INSERT OR UPDATE</literal>) 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.)
+  </para>
+
+  <para>
+   There is an example in <filename>autoinc.example</filename>.
+  </para>
+
+ </sect2>
+
+ <sect2>
+  <title>insert_username &mdash; Functions for Tracking Who Changed a Table</title>
+
+  <para>
+   <function>insert_username()</function> 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.
+  </para>
+
+  <para>
+   To use, create a <literal>BEFORE INSERT</literal> and/or <literal>UPDATE</literal>
+   trigger using this function.  Specify a single trigger
+   argument: the name of the text column to be modified.
+  </para>
+
+  <para>
+   There is an example in <filename>insert_username.example</filename>.
+  </para>
+
+ </sect2>
+
+ <sect2>
+  <title>moddatetime &mdash; Functions for Tracking Last Modification Time</title>
+
+  <para>
+   <function>moddatetime()</function> is a trigger that stores the current
+   time into a <type>timestamp</type> field.  This can be useful for tracking
+   the last modification time of a particular row within a table.
+  </para>
+
+  <para>
+   To use, create a <literal>BEFORE UPDATE</literal>
+   trigger using this function.  Specify a single trigger
+   argument: the name of the column to be modified.
+   The column must be of type <type>timestamp</type> or <type>timestamp with
+   time zone</type>.
+  </para>
+
+  <para>
+   There is an example in <filename>moddatetime.example</filename>.
+  </para>
+
+ </sect2>
+
+</sect1>