更新计数器触发 PostgreSql

Question

我有一张这样的桌子

-----------------------------------------------------------------------------------
id                                    | notification_sent | times_notification_sent
-----------------------------------------------------------------------------------
4a1717a2-6e1e-4af6-aa34-8262899aa060  | t                 | 0

这里发送的通知是布尔字段，times_notification_sent 是 int。我正在尝试创建触发器，当 notification_sent 从 true 更改为 false 时，times_notification_sent 将增加 1。

我正在使用以下函数和触发器，但它不起作用。

CREATE OR REPLACE FUNCTION update_sent_counter_for_watch()  RETURNS TRIGGER 
LANGUAGE plpgsql
AS $$ BEGIN
IF OLD.notification_sent IS TRUE AND NEW.notification_sent IS FALSE THEN
   UPDATE "watch" SET "times_notification_sent" = "times_notification_sent" + 1 WHERE "id" = OLD."id";
END IF;
END;
$$;

CREATE TRIGGER "update_times_sent_counter" AFTER UPDATE OF "times_notification_sent" ON "public"."watch"
FOR EACH ROW
WHEN (OLD.notification_sent IS DISTINCT FROM NEW.notification_sent)
EXECUTE PROCEDURE "public"."update_sent_counter_for_watch"();

Answer 1

你有两个错误：

您不需要update，只需分配新值：

CREATE OR REPLACE FUNCTION update_sent_counter_for_watch()  
  RETURNS TRIGGER 
  LANGUAGE plpgsql
AS 
$$ 
BEGIN
  IF OLD.notification_sent IS TRUE AND NEW.notification_sent IS FALSE THEN
    new.times_notification_sent := old.times_notification_sent + 1;
  END IF;
  RETURN new;
END;
$$;

而且您不能更改after update 触发器中的值，您需要将其更改为before 触发器：

CREATE TRIGGER "update_times_sent_counter" BEFORE UPDATE OF "times_notification_sent" 
  ON "public"."watch"
  FOR EACH ROW
WHEN (OLD.notification_sent IS DISTINCT FROM NEW.notification_sent)
EXECUTE PROCEDURE "public"."update_sent_counter_for_watch"();