CLR Stored Procedure needs a Sql Server execution thread

Question

I've a CLR trigger, which calls a Stored Procedure with BeginInvoke. In the Stored Procedure I try to call an SqlComman, but I get: The requested operation requires a Sql Server execution thread. The current thread was started by user code or other non-Sql Server engine code.

I have to do this things in the SP, and I have to call the SP with BeginInvoke, because of the waiting.

The code:

[SqlProcedure()]
public static void MySendData( String crudType, String sourceTable, ... ) {
    SqlCommand sqlDeleteComm;

    String temp = String.Empty;

    using( SqlConnection conn = new SqlConnection( "context connection=true" ) ) {

        sqlDeleteComm = new SqlCommand( "DELETE FROM #TEMP_TABLE" );
        sqlDeleteComm.Connection = conn;

        try {
            conn.Open();
            sqlDeleteComm.ExecuteNonQuery();
            conn.Close();
        } catch( Exception ex ) {
            // --- here ---
            // The requested operation requires a Sql Server execution thread.  The current thread was started by user code or other non-Sql Server engine code.
        }
    }
    ...
}

[Microsoft.SqlServer.Server.SqlTrigger( Name = "MyTrigger", Target = "MyTable", Event = "FOR UPDATE, INSERT, DELETE" )]
public static void MyTrigger() {
    SqlTriggerContext myContext = SqlContext.TriggerContext;
    MyDelagate d;
    SqlCommand sqlComm;
    SqlDataReader reader;

    if( connection.State != ConnectionState.Open ) {
        connection.Open();
    }

    switch( myContext.TriggerAction ) {
        case TriggerAction.Update:
            sqlComm = new SqlCommand( "SELECT X, Y FROM Inserted" );
            sqlComm.Connection = connection;

            reader = sqlComm.ExecuteReader();
            try {
                reader.Read();
                d = new MyDelagate( MySendData );
                d.BeginInvoke( "Update", "MyTable", ( Int32 )reader[ 0 ], ( Int32 )reader[ 1 ], null, null );
            } catch( Exception ex ) {
            } finally {
                reader.Close();
            }
            break;
            ...
    }
}

How could I, for all that call SQL queries in the SP?

Answer 1

You can't use the context connection outside of the thread SQL Server runs your CLR code in; this is to ensure reliability of the server - SQL Server uses custom CLR hosting, and I'm surprised it allowed you to spin your own thread at all. You can call MySendData from MyTrigger with T-SQL, using standard ADO.NET SqlCommand on the context SqlConnection, but there is no way for it to run in a separate thread. If you really want asynchrony/parrallelism on the database level, look into SQL Server Broker.

Answer 2

If you can avoid using the context connection you can circumvent this issue. Creating a new SqlConnection with a conventional connection string (with the Enlist option set to false to prevent usage of the same transaction context if necessary) will allow you to use multithreading in a SQL CLR context.