F.39. tcn

tcn模块提供一个触发器函数，它通知监听者有关它所附着的任意表上的改变。它必须被用作一个行级AFTER触发器。

在一个CREATE TRIGGER语句中只可以为该函数提供一个参数，并且是可选的。如果提供该参数，它将被作为用于通知的频道名。如果忽略它，频道名将使用tcn。

通知的负载由表名、一个指示所执行操作类型的字母以及用于主键列的列名/值对构成。每一部分都用逗号与下一部分隔开。为了便于解析对正则表达式的使用，表和列名总是被包裹在双引号内，并且数据值总是被包裹在单引号内。嵌入的引号都被双写。

下面是使用该扩展的简单例子。

test=# create table tcndata
test-#   (
test(#     a int not null,
test(#     b date not null,
test(#     c text,
test(#     primary key (a, b)
test(#   );
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.