I've tried setting up an SQL Dependency to fire on a "Count Rows" query (written in C#, SQL Server 2008 Express), but after the original subscription SQLNotificationType goes, the event handler never seems to want to fire again (despite rows being added, and I've checked the SQL and it's returning the expected value...).
My code is below. Any thoughts are much appreciated!
EDIT: The project that this code is in is a WPF program. I have this particular code stored in a separate class, which my WPF program creates an instance of in an 'Initialized' event handler. I then have a method in this class that basically calls ConnectToDatabase() first, and then calls SetupSQLDependency().
EDIT 2: As a side note, this program is a WPF which I was hoping to distribute to a few users. The goal was to have the WPF update with certain information whenever new rows were added to a database. I thought that this would be the best way to go about it, as opposed to always querying the database.
private void ConnectToDatabase()
{
//This method is the first to be called, and is the entry
// point into my SQL database code.
databaseConnection = new SqlConnection(connectionString);
// Setup command used in SqlDependecy
SqlCommand tempCmd = new SqlCommand();
tempCmd.Connection = databaseConnection;
tempCmd.CommandText = "SELECT COUNT(ID) FROM [Example].[dbo].[ExampleTable]";
sqlCmd = tempCmd;
try
{ databaseConnection.Open(); }
catch (Exception e)
{ writeDebug(e.ToString()); }
}
private void SetupSQLDependency()
{
SqlDependency.Stop(connectionString);
SqlDependency.Start(connectionString);
sqlCmd.Notification = null;
// create new dependency for SqlCommand
SqlDependency sqlDep = new SqlDependency(sqlCmd);
sqlDep.OnChange += new OnChangeEventHandler(sqlDep_OnChange);
SqlDataReader reader = sqlCmd.ExecuteReader();
}
private void sqlDep_OnChange(object sender, SqlNotificationEventArgs e)
{
// FROM: http://msdn.microsoft.com/en-us/a52dhwx7.aspx
if (e.Type == SqlNotificationType.Change)
{
//++++++ THIS IS THE BLOCK THAT IS NEVER TRIGGERED ++++++//
// Have to remove this as it only work's once
SqlDependency sqlDep = sender as SqlDependency;
sqlDep.OnChange -= sqlDep_OnChange;
// Resetup Dependecy
SetupSQLDependency();
}
else if (e.Type == SqlNotificationType.Subscribe)
{
double te = 12; // Used this just to test a break... code is useless
}
}
Pageand is called in theOnLoadevent, then you have to remember that your page class is only alive for a split second while the page is being rendered and then a whole new class is instantiated for each request. So your event subscription, and thesqlCmdvariable instance are not kept around (and theoeretically are causing mem leaks).SqlNotificationType.Changefire once and only once, or never at all?SQL Express, which jumped out at me as I swear it does not support the Broker Service you require for the SQLDependencies, but I am having real trouble finding a definitive statement of such on MSDN. I'll keep digging, but I'd recommend it as something to investigate. We have almost identical code to yours running on SQL Server 2008 Developer and Standard editions, we did not try Express because of this somewhat elusive statement regarding the Express edition...