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Devart.Data.SqlServer Namespace / SqlCommand Class / BeginExecuteXmlReader Method / BeginExecuteXmlReader() Method
Example

In This Topic
    BeginExecuteXmlReader() Method
    In This Topic
    Starts an asynchronous invocation of an ExecuteXmlReader method.
    Syntax
    'Declaration
     
    Public Overloads Function BeginExecuteXmlReader() As IAsyncResult
    public IAsyncResult BeginExecuteXmlReader()

    Return Value

    An System.IAsyncResult interface that represents the asynchronous operation started by calling this method.
    Remarks

    BeginExecuteXmlReader method enables you to execute a Transact-SQL statement, that has a valid FOR XML clause or returns NTEXT or NVARCHAR data that contains valid XML, or the contents of a column defined with the XML data type, without having current thread blocked. In other words, your program can continue execution while the query runs on a database so you do not have to wait for it.

    Refer to "Asynchronous Query Execution" article for detailed information.

    To start running a query, you have to call BeginExecuteXmlReader method, which in turn invokes appropriate actions in another thread. Return value of this method must be assigned to an System.IAsyncResult object. After executing this method, the program flow continues.

    When you are ready to accept query results, call EndExecuteXmlReader. If at the moment you call this function the query execution has not yet been finished, application stops and waits till the function returns. Then you can treat a System.Xml.XmlReader in a common way.

    Example
    In the example below the easiest way of executing an asynchronous operation is shown. First, all components are set up and a connection is opened. Second, a data retrieval operation is started. The operation state (done or in progress) is checked and a report is written to the console. At last query results are sent to Devart.Common.DbDataReader and rendered to the console.
    public void Async_Exec(DbConnectionBase myConnection)
    {
      DbCommandBase myCommand = (DbCommandBase)myConnection.CreateCommand();
      myCommand.CommandText = "SELECT * FROM Test.Dept";
      Console.WriteLine("Starting asynchronous retrieval of data...");
      myConnection.Open();
      IAsyncResult cres = myCommand.BeginExecuteReader();
      if (cres.IsCompleted)
        Console.WriteLine("Completed.");
      else
        Console.WriteLine("Have to wait for operation to complete...");
      DbDataReader myReader = myCommand.EndExecuteReader(cres);
      try
      {
        while (myReader.Read())
        {
          Console.WriteLine(myReader.GetInt32(0) + " " + myReader.GetString(1) + " " + myReader.GetString(2));
        }
      }
      finally
      {
        myReader.Close();
        myConnection.Close();
      }
    }
    Public Sub Async_Exec(ByVal myConnection As DbConnectionBase)
      Dim myCommand As DbCommandBase = myConnection.CreateCommand()
      myCommand.CommandText = "SELECT * FROM Test.Dept"
      Console.WriteLine("Starting asynchronous retrieval of data...")
      myConnection.Open()
      Dim cres As IAsyncResult = myCommand.BeginExecuteReader()
      If cres.IsCompleted Then
        Console.WriteLine("Completed.")
      Else
        Console.WriteLine("Have to wait for operation to complete...")
      End If
      Dim myReader As DbDataReader = myCommand.EndExecuteReader(cres)
      Try
        While myReader.Read()
          Console.WriteLine(String.Concat(myReader.GetInt32(0).ToString(), " ", myReader.GetString(1), " ", myReader.GetString(2)))
        End While
      Finally
        myReader.Close()
        myConnection.Close()
      End Try
    End Sub
    Requirements

    Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

    See Also