78 lines
3.0 KiB
Plaintext
78 lines
3.0 KiB
Plaintext
<!-- doc/src/sgml/tcn.sgml -->
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<sect1 id="tcn" xreflabel="tcn">
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<title>tcn — a trigger function to notify listeners of changes to table content</title>
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<indexterm zone="tcn">
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<primary>tcn</primary>
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</indexterm>
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<indexterm zone="tcn">
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<primary>triggered_change_notification</primary>
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</indexterm>
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<para>
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The <filename>tcn</filename> module provides a trigger function that notifies
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listeners of changes to any table on which it is attached. It must be
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used as an <literal>AFTER</literal> trigger <literal>FOR EACH ROW</literal>.
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</para>
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<para>
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This module is considered <quote>trusted</quote>, that is, it can be
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installed by non-superusers who have <literal>CREATE</literal> privilege
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on the current database.
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</para>
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<para>
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Only one parameter may be supplied to the function in a
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<literal>CREATE TRIGGER</literal> statement, and that is optional. If supplied
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it will be used for the channel name for the notifications. If omitted
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<literal>tcn</literal> will be used for the channel name.
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</para>
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<para>
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The payload of the notifications consists of the table name, a letter to
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indicate which type of operation was performed, and column name/value pairs
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for primary key columns. Each part is separated from the next by a comma.
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For ease of parsing using regular expressions, table and column names are
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always wrapped in double quotes, and data values are always wrapped in
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single quotes. Embedded quotes are doubled.
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</para>
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<para>
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A brief example of using the extension follows.
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<programlisting>
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test=# create table tcndata
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test-# (
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test(# a int not null,
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test(# b date not null,
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test(# c text,
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test(# primary key (a, b)
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test(# );
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CREATE TABLE
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test=# create trigger tcndata_tcn_trigger
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test-# after insert or update or delete on tcndata
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test-# for each row execute function triggered_change_notification();
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CREATE TRIGGER
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test=# listen tcn;
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LISTEN
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test=# insert into tcndata values (1, date '2012-12-22', 'one'),
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test-# (1, date '2012-12-23', 'another'),
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test-# (2, date '2012-12-23', 'two');
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INSERT 0 3
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Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
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Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
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Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
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test=# update tcndata set c = 'uno' where a = 1;
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UPDATE 2
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Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
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Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
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test=# delete from tcndata where a = 1 and b = date '2012-12-22';
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DELETE 1
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Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
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</programlisting>
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</para>
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</sect1>
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