更改表数据时如何在前端触发NOTIFICATION事件 [英] How to fire NOTIFICATION event in front end when table data gets changed

问题描述

我正在尝试利用vb.net中 Npgsql 给定的通知事件。我对这种机制有部分了解，我了解到的是，只要更改了特定表的数据，就会触发其 trigger ，因此在其中的触发，我们可以通知到前端了解数据更改。

I am trying to make use of the Notification event given by Npgsql in vb.net. I partially got an idea about this mechanism, what i learned was, when ever a particular table's data has got changed, its trigger will be fired, so inside that trigger we can notify to the front end about the data change.

我设法在前端运行以下代码

I managed to run this following code in my front end

Public Sub test()

    Dim conn = New NpgsqlConnection("Server=servername;port=portNo; _
               User Id=UID;pwd=PWD;DataBase=DB;")
    conn.Open()

    Dim command = New NpgsqlCommand("listen notifytest;", conn)
    command.ExecuteNonQuery()


    AddHandler conn.Notification, AddressOf NotificationSupportHelper

    command = New NpgsqlCommand("notify notifytest;", conn)
    command.ExecuteNonQuery()



End Sub

Private Sub NotificationSupportHelper(ByVal sender As Object, _
                                      ByVal e As NpgsqlNotificationEventArgs)

'Notified here.

End Sub

上面的代码可以解决所有问题。但是我想知道的是如何创建触发器，它将通知有关前端数据更改的信息结果是我前端的 Notification事件被解雇了？以及我需要在何处致电收听 ？？我需要为每个查询的执行调用监听吗？有人可以用一些示例代码来澄清我的疑问吗？？

The above code is working with out any issues. But what i am trying to know is how to create a trigger which will notifies about the data change to the front end as a result the Notification event in my front end gets fired ? and where do i need to call listen.? Do i need to call listen for each query's execution .? Can any body will clarify my doubts with some sample codes.?

推荐答案

前端：

Public Sub test()

Dim conn = New NpgsqlConnection(" Server=server; port=portno;User Id=uid; pwd=pwd; DataBase=Db; ")
conn.Open()

Dim command = New NpgsqlCommand("listen notifytest;", conn)
command.ExecuteNonQuery()

AddHandler conn.Notification, AddressOf NotificationSupportHelper


command = New NpgsqlCommand("update testtable set field='test' where id=1", conn)
Dim x As NpgsqlDataReader = command.ExecuteReader
End Sub

Private Sub NotificationSupportHelper(ByVal sender As Object, ByVal e As NpgsqlNotificationEventArgs)
    MsgBox(e.Condition)
End Sub

TRIGGER：

CREATE OR REPLACE FUNCTION testingNotify()
  RETURNS trigger AS
$BODY$ 
    begin
       notify notifytest;
       return null;
    end;     
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION testingNotify() OWNER TO testserver;

以上给出的触发器将被解雇插入或删除或更新在表<$中c $ c> testtable 。所以在上面的代码中，在名为 test 的过程中，我编写了一个查询更新表tabletest 的查询，在执行查询时，会调用 NotificationSupportHelper 。

The trigger given above will get fired if Insert or delete or update happens in the table testtable. so in the above code, inside the procedure named test, i had written a query for updating the table tabletest, so while executing the query the NotificationSupportHelper gets called.

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