6

I am trying to detect if any changes been made to SQL table I'm working with. I need to specify the search by selecting specific records only, and for this reason I need to use string parameter. I understand that according to this MSDN document:

The statement must not contain conditional statements that cannot change and cannot return results (for example, WHERE 1=0)

Is there any way to include string parameter when using SqlDependency?

If it means something, I use SQL Server 2012 and VS 2010

Here is my code so far.

Code output: "The above notification query is not valid.":

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


namespace AutoRegSession
{
    public partial class RoomActiveSession : Form
    {     
        public Timer timer = new Timer();         //Timer to measure update times
        public string SessionID;                  //String to hold selected sessionID
        string ConnStr = "Data Source=DUZY;Initial Catalog=AutoRegSQL;Integrated Security=True";    

        SqlDependency dependency;

        public RoomActiveSession()
        {
            SqlDependency.Start(ConnStr);
            InitializeComponent();
        }


        private void btn_Exit_Click(object sender, EventArgs e)
        {
            SqlDependency.Stop(ConnStr);
            timer.Enabled = false;  //Disable timer
            timer.Stop();           //Stop timer
            Application.Exit();     //Close application
        }

        //Check for table updates every 3 seconds
        private void timer_Tick(object sender, EventArgs e)
        {
            refreshDGV();
        }

        //SQL query that returns current/updated attendance result list for the given SessionID
        public void refreshDGV()
        {
            DataTable queryResult = new DataTable();   

            SqlConnection MyConn = new SqlConnection(ConnStr);      //Use connection string

            string query = @"SELECT TagID, SessionID, ScanningTime" +
               " FROM Attendance " +
               " WHERE SessionID = @SessionID ";

            SqlCommand command = new SqlCommand(query, MyConn);                             

            command.Parameters.Add("SessionID", SqlDbType.Char).Value = SessionID;    

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

            //Subscribe to the SqlDependency event
            dependency.OnChange += new OnChangeEventHandler(OnDependencyChange);

            SqlDataAdapter adapter = new SqlDataAdapter(command);                           

            adapter.Fill(queryResult);                                                      

            DGVSetDataSouce(queryResult);                                                   

        }

        //Handler method for SQL Dependecy
        private void OnDependencyChange(object sender, SqlNotificationEventArgs eventArgs)
        {
            if (eventArgs.Info == SqlNotificationInfo.Invalid)
            {
                MessageBox.Show("The above notification query is not valid.");
            }
            else
            {
                MessageBox.Show("Notification Info: " + eventArgs.Info);
                MessageBox.Show("Notification source: " + eventArgs.Source);
                MessageBox.Show("Notification type: " + eventArgs.Type);
            }
        }

        //Create and start the timer
        public void SetTimer()
        {
            timer.Interval = 3000;
            timer.Tick += new EventHandler(timer_Tick);
            timer.Enabled = true;
            timer.Start();
        }
    }
}
4

1 回答 1

1

它应该工作。

问题可能是您没有为表 n SQL 查询指定两个部分名称。

SELECT 语句中的投影列必须明确声明，并且表名必须用两部分名称限定。

它只是说当存在在任何情况下都无法返回结果的 where 子句时它不起作用。

于 2013-09-22T13:49:57.387 回答