F.37. tcn

tcn模块提供了一个触发器函数，通知监听器它附着的任何表有修改。 它必须作为一个AFTER触发器FOR EACH ROW使用。

在一个CREATE TRIGGER语句中只需要提供一个参数到函数，并且是可选的。 如果提供了，它将用于通知的通道名。如果省略了，tcn将用作通道名。

通知的负载包括表名、一个表明执行了什么操作类型的字母和主键字段的字段名/值对。 每个部分用一个逗号分隔开。为了使正则表达式的分析简单化，表和字段名总是包含在双引号中， 数据值总是包含在单引号中。双引号里的引号需要写两次。

使用该扩展的一个简单的例子如下所示。

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.