EndExecuteReader Method (DbCommandBase)

In This Topic

Ends an asynchronous invocation of the System.Data.Common.DbCommandBase.ExecuteReader method.

Syntax

Visual Basic
C#

'Declaration
 
Public Function EndExecuteReader( _
   ByVal result As IAsyncResult _
) As DbDataReader

public DbDataReader EndExecuteReader( 
   IAsyncResult result
)

Parameters

result: The System.IAsyncResult returned by BeginExecuteReader.

Return Value

A DbDataReaderBase object.

Remarks

The function ends an asynchronous execution of a query that is started with BeginExecuteReader. A pair of asynchronous functions (BeginExecuteReader and EndExecuteReader) can be used instead of the synchronous function System.Data.Common.DbCommand.ExecuteReader to gain more performance and flexibility in your application.

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

Example

In the example below an 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 DbDataReaderBase and rendered to the console.

csharp

public void Async_Exec(DbConnectionBase myConnection)
{
  DbCommandBase myCommand = (DbCommandBase)myConnection.CreateCommand();
  myCommand.CommandText = "SELECT DeptNo, DName, Loc FROM Dept";
  Console.WriteLine("Starting asynchronous retrieval of data...");
  myConnection.Open();
  IAsyncResult cres = myCommand.BeginExecuteReader(null, null, CommandBehavior.Default);
  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).ToString() + " " + myReader.GetString(1) + " " + myReader.GetString(2));
    }
  }
  finally
  {
    myReader.Close();
    myConnection.Close();
  }
}

Visual Basic

Public Sub Async_Exec(ByVal myConnection As DbConnectionBase)
  Dim myCommand As DbCommandBase = myConnection.CreateCommand()
  myCommand.CommandText = "SELECT DeptNo, DName, Loc FROM Dept"
  Console.WriteLine("Starting asynchronous retrieval of data...")
  myConnection.Open()
  Dim cres As IAsyncResult = myCommand.BeginExecuteReader(Nothing, Nothing, CommandBehavior.Default)
  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

Reference

DbCommandBase Class
DbCommandBase Members

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