140 lines
5.2 KiB
Plaintext
140 lines
5.2 KiB
Plaintext
<!-- doc/src/sgml/contrib-spi.sgml -->
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<sect1 id="contrib-spi" xreflabel="spi">
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<title>spi — Server Programming Interface features/examples</title>
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<indexterm zone="contrib-spi">
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<primary>SPI</primary>
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<secondary>examples</secondary>
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</indexterm>
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<para>
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The <application>spi</application> module provides several workable examples
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of using the <link linkend="spi">Server Programming Interface</link>
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(<acronym>SPI</acronym>) and triggers. While these functions are of
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some value in
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their own right, they are even more useful as examples to modify for
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your own purposes. The functions are general enough to be used
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with any table, but you have to specify table and field names (as described
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below) while creating a trigger.
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</para>
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<para>
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Each of the groups of functions described below is provided as a
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separately-installable extension.
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</para>
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<sect2 id="contrib-spi-refint">
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<title>refint — Functions for Implementing Referential Integrity</title>
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<para>
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<function>check_primary_key()</function> and
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<function>check_foreign_key()</function> are used to check foreign key constraints.
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(This functionality is long since superseded by the built-in foreign
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key mechanism, of course, but the module is still useful as an example.)
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</para>
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<para>
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<function>check_primary_key()</function> checks the referencing table.
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To use, create a <literal>BEFORE INSERT OR UPDATE</literal> trigger using this
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function on a table referencing another table. Specify as the trigger
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arguments: the referencing table's column name(s) which form the foreign
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key, the referenced table name, and the column names in the referenced table
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which form the primary/unique key. To handle multiple foreign
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keys, create a trigger for each reference.
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</para>
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<para>
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<function>check_foreign_key()</function> checks the referenced table.
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To use, create a <literal>BEFORE DELETE OR UPDATE</literal> trigger using this
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function on a table referenced by other table(s). Specify as the trigger
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arguments: the number of referencing tables for which the function has to
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perform checking, the action if a referencing key is found
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(<literal>cascade</literal> — to delete the referencing row,
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<literal>restrict</literal> — to abort transaction if referencing keys
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exist, <literal>setnull</literal> — to set referencing key fields to null),
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the triggered table's column names which form the primary/unique key, then
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the referencing table name and column names (repeated for as many
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referencing tables as were specified by first argument). Note that the
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primary/unique key columns should be marked NOT NULL and should have a
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unique index.
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</para>
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<para>
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There are examples in <filename>refint.example</filename>.
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</para>
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</sect2>
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<sect2 id="contrib-spi-autoinc">
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<title>autoinc — Functions for Autoincrementing Fields</title>
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<para>
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<function>autoinc()</function> is a trigger that stores the next value of
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a sequence into an integer field. This has some overlap with the
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built-in <quote>serial column</quote> feature, but it is not the same:
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<function>autoinc()</function> will override attempts to substitute a
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different field value during inserts, and optionally it can be
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used to increment the field during updates, too.
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</para>
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<para>
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To use, create a <literal>BEFORE INSERT</literal> (or optionally <literal>BEFORE
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INSERT OR UPDATE</literal>) trigger using this function. Specify two
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trigger arguments: the name of the integer column to be modified,
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and the name of the sequence object that will supply values.
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(Actually, you can specify any number of pairs of such names, if
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you'd like to update more than one autoincrementing column.)
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</para>
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<para>
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There is an example in <filename>autoinc.example</filename>.
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</para>
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</sect2>
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<sect2 id="contrib-spi-insert-username">
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<title>insert_username — Functions for Tracking Who Changed a Table</title>
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<para>
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<function>insert_username()</function> is a trigger that stores the current
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user's name into a text field. This can be useful for tracking
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who last modified a particular row within a table.
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</para>
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<para>
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To use, create a <literal>BEFORE INSERT</literal> and/or <literal>UPDATE</literal>
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trigger using this function. Specify a single trigger
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argument: the name of the text column to be modified.
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</para>
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<para>
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There is an example in <filename>insert_username.example</filename>.
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</para>
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</sect2>
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<sect2 id="contrib-spi-moddatetime">
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<title>moddatetime — Functions for Tracking Last Modification Time</title>
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<para>
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<function>moddatetime()</function> is a trigger that stores the current
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time into a <type>timestamp</type> field. This can be useful for tracking
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the last modification time of a particular row within a table.
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</para>
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<para>
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To use, create a <literal>BEFORE UPDATE</literal>
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trigger using this function. Specify a single trigger
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argument: the name of the column to be modified.
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The column must be of type <type>timestamp</type> or <type>timestamp with
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time zone</type>.
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</para>
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<para>
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There is an example in <filename>moddatetime.example</filename>.
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</para>
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</sect2>
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</sect1>
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