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>F.36. tcn</A
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> The <TT
CLASS="FILENAME"
>tcn</TT
> module provides a trigger function that notifies
listeners of changes to any table on which it is attached. It must be
used as an <TT
CLASS="LITERAL"
>AFTER</TT
> trigger <TT
CLASS="LITERAL"
>FOR EACH ROW</TT
>.
</P
><P
> Only one parameter may be supplied to the function in a
<TT
CLASS="LITERAL"
>CREATE TRIGGER</TT
> statement, and that is optional. If supplied
it will be used for the channel name for the notifications. If omitted
<TT
CLASS="LITERAL"
>tcn</TT
> will be used for the channel name.
</P
><P
> The payload of the notifications consists of the table name, a letter to
indicate which type of operation was performed, and column name/value pairs
for primary key columns. Each part is separated from the next by a comma.
For ease of parsing using regular expressions, table and column names are
always wrapped in double quotes, and data values are always wrapped in
single quotes. Embedded quotes are doubled.
</P
><P
> A brief example of using the extension follows.
</P><PRE
CLASS="PROGRAMLISTING"
>test=# create table tcndata
test-# (
test(# a int not null,
test(# b date not null,
test(# c text,
test(# primary key (a, b)
test(# );
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "tcndata_pkey" for table "tcndata"
CREATE TABLE
test=# create trigger tcndata_tcn_trigger
test-# after insert or update or delete on tcndata
test-# for each row execute procedure triggered_change_notification();
CREATE TRIGGER
test=# listen tcn;
LISTEN
test=# insert into tcndata values (1, date '2012-12-22', 'one'),
test-# (1, date '2012-12-23', 'another'),
test-# (2, date '2012-12-23', 'two');
INSERT 0 3
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",I,"a"='2',"b"='2012-12-23'" received from server process with PID 22770.
test=# update tcndata set c = 'uno' where a = 1;
UPDATE 2
Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.
Asynchronous notification "tcn" with payload ""tcndata",U,"a"='1',"b"='2012-12-23'" received from server process with PID 22770.
test=# delete from tcndata where a = 1 and b = date '2012-12-22';
DELETE 1
Asynchronous notification "tcn" with payload ""tcndata",D,"a"='1',"b"='2012-12-22'" received from server process with PID 22770.</PRE
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