如何保持 sql 依赖项发挥其作用 [英] how to keep sql dependency doing the its purpose

问题描述

我有一个控制台应用程序.

I have a console application.

我想继续观察我的数据库表中特定列的变化.

I wanna keep watching the changes on a specific column in my database table.

我通过互联网阅读，发现 sql 依赖对我的目的有好处.我开始了解它并做了以下事情:

I read through internet and I have found that sql dependency is good for my purpose. I started learning about it and I did the following:

1. 创建一个类.
2. 在构造函数中，我调用了静态函数start，并调用了一个具有所有sql依赖设置的函数.

1. create a class.
2. In the constructor, I called the static function start and I called a function that has all the sql dependency settings.

我的问题

当我使用 start 点击 Visual Studio 2013 运行应用程序时，应用程序运行然后停止.但是，我需要的是应用程序开始工作并持续关注我的数据库表中的更改.

My problem

When I run the application using the start click on visual studio 2013, the apps works and then stops. However, what I need is that the apps starts working and keep watching for changes in my database's table.

你能帮帮我吗?

这是一个非常非常简单的c#代码.

This is a very very simple c# code.

public class MyListener
    {
        public MyListener()
        {
            SqlDependency.Start(getConnectionString());
            this.listen();
        }

        private string getConnectionString()
        {
            return ConfigurationManager.ConnectionStrings["popup"].ConnectionString.ToString();
        }
        private void listen()
        {
            string query = "SELECT CallerID FROM TransferToSIP WHERE hasBeenRead = 0";
            SqlConnection con = new SqlConnection(getConnectionString());
            SqlCommand cmd = new SqlCommand(query, con);
            con.Open();
            using (cmd)
            {
                SqlDependency dependency = new SqlDependency(cmd);
                dependency.OnChange += new
                   OnChangeEventHandler(OnDependencyChange);
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                }
            }
        }
        void OnDependencyChange(object sender, SqlNotificationEventArgs e)
        {
            Console.WriteLine("Roma");
        }
        void Termination()
        {
            SqlDependency.Stop(getConnectionString());
            Console.Read();
        }

推荐答案

问题在于没有重新订阅.您应该在 OnDependencyChange 中调用 listen 方法.我知道这很奇怪，但它是 SqlDependency 类.

The problem is in absence of the resubscruption. You should call the listen method inside of OnDependencyChange. I know that it is weird, but it is the SqlDependency class.

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