更改数据集时，SqlDependency 不会触发 OnChange 事件

Question

我是 SQL Server 查询通知概念的新手，我需要一些时间来理解它。

我的目标是创建一个 Windows 服务应用程序，当 SQL Server 表发生更改时它会收到通知。我遵循了this 指南，这对我开始很有帮助。

但是我无法获得预期的结果。我的 Windows 服务应用程序中的 OnStart() 方法如下所示：

protected override void OnStart(string[] args)
{
        eventLog1.WriteEntry("Service Started");

        serviceRun = false;

        SqlClientPermission perm = new SqlClientPermission(System.Security.Permissions.PermissionState.Unrestricted);

        try
        {
            perm.Demand();
            eventLog1.WriteEntry("permission granted");
        }
        catch (System.Exception)
        {
            eventLog1.WriteEntry("permission denied");
        }

        try
        {
            connstr = "Data Source=THSSERVER-LOCAL;Initial Catalog=ET;User ID=mujtaba;Password=ths123";

            connection = new SqlConnection(connstr);

            SqlCommand command = new SqlCommand("select * from dbo.Customer_FileUploads", connection);

            // Create a dependency and associate it with the SqlCommand.
            SqlDependency dependency = new SqlDependency(command);

            // Maintain the reference in a class member.
            // Subscribe to the SqlDependency event.
            dependency.OnChange += Dependency_OnChange;

            SqlDependency.Start(connstr);

            connection.Open();

            // Execute the command.
            using (SqlDataReader reader = command.ExecuteReader())
            {
                if (reader.HasRows)
                {
                    while (reader.Read())
                    {
                        //eventLog1.WriteEntry("reading data");
                    }
                }
                else
                {
                    eventLog1.WriteEntry("No rows found.");
                }
                reader.Close();
            }
        }
        catch (Exception e)
        {
            eventLog1.WriteEntry("Error Message: " + e.Message);
        }
}

订阅了SqlDependency 的事件，如下所示：

private void Dependency_OnChange(object sender, SqlNotificationEventArgs e)
{
    // Handle the event.
    eventLog1.WriteEntry("data changed");
}

OnStop() 方法如下所示：

protected override void OnStop()
{
        SqlDependency.Stop(connstr);
        connection.Close();
        eventLog1.WriteEntry("In onStop.");
}

我在我的数据库中将ENABLE_BROKER 设置为true。最终结果是，服务运行并创建了以下日志：

"Service Started"
"permission granted"
"data changed"

但是，当我将新数据插入表中时，OnChange() 事件不会触发并且不会创建新日志。此外，当我停止并再次启动服务时，即使没有插入新数据，也会触发OnChange()。

谁能帮我理解这个过程？

Answer 1

SqlDependency 在事件触发后被删除，因此您需要使用依赖项再次执行命令。下面是一个控制台应用程序示例，它将再次订阅，除非通知是由于错误引起的。

using System;
using System.Data;
using System.Data.SqlClient;

namespace SqlDependencyExample
{
    class Program
    {

        static string connectionString = @"Data Source=.;Initial Catalog=YourDatabase;Application Name=SqlDependencyExample;Integrated Security=SSPI";

        static void Main(string[] args)
        {

            SqlDependency.Start(connectionString);

            getDataWithSqlDependency();

            Console.WriteLine("Waiting for data changes");
            Console.WriteLine("Press enter to quit");
            Console.ReadLine();

            SqlDependency.Stop(connectionString);

        }

        static DataTable getDataWithSqlDependency()
        {

            using (var connection = new SqlConnection(connectionString))
            using (var cmd = new SqlCommand("SELECT Col1, Col2, Col3 FROM dbo.MyTable;", connection))
            {

                var dt = new DataTable();

                // Create dependency for this command and add event handler
                var dependency = new SqlDependency(cmd);
                dependency.OnChange += new OnChangeEventHandler(onDependencyChange);

                // execute command to get data
                connection.Open();
                dt.Load(cmd.ExecuteReader(CommandBehavior.CloseConnection));

                return dt;

            }

        }

        // Handler method
        static void onDependencyChange(object sender,
           SqlNotificationEventArgs e)
        {

            Console.WriteLine($"OnChange Event fired. SqlNotificationEventArgs: Info={e.Info}, Source={e.Source}, Type={e.Type}.");

            if ((e.Info != SqlNotificationInfo.Invalid)
                && (e.Type != SqlNotificationType.Subscribe))
            {
                //resubscribe
                var dt = getDataWithSqlDependency();

                Console.WriteLine($"Data changed. {dt.Rows.Count} rows returned.");
            }
            else
            {
                Console.WriteLine("SqlDependency not restarted");
            }

        }


    }
}