服務器端AsyncPattern調用SQL服務器

Question

我嘗試在WCF數據服務中實現'AsyncPattern'。我在界面中定義了兩種方法BeginGetExperiments（...）和EndGetExperiments（...），並實現瞭如下所示的方法。

public class GmdProfileService : IGmdProfileService 
{ 
IAsyncResult IGmdProfileService.BeginGetExperiments(AsyncCallback callback, object state) 
    { 
     //IAsyncResult res = Experiment.GetExperimentsAsync(callback, state, Properties.Settings.Default.gmdConnectionString); 
     //return res; 

     System.Data.SqlClient.SqlConnectionStringBuilder csb = new System.Data.SqlClient.SqlConnectionStringBuilder(Properties.Settings.Default.gmdConnectionString); 
     csb.AsynchronousProcessing = true; 
     System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(csb.ConnectionString); 
     conn.Open(); 
     System.Data.SqlClient.SqlCommand cmd = conn.CreateCommand(); 
     cmd = conn.CreateCommand(); 
     cmd.CommandText = "SELECT id, name, comment, date, doi FROM tf.TagList WITH(NOLOCK) WHERE proprietary=0;"; 
     cmd.CommandType = System.Data.CommandType.Text; 
     return new SqlCommandAsyncResult(cmd, callback, state); 
    } 

    public List<Experiment> EndGetExperiments(IAsyncResult result) 
    { 
     List<Experiment> res = new List<Experiment>(); 
     SqlCommandAsyncResult myresult = result as SqlCommandAsyncResult; 
     using (System.Data.SqlClient.SqlDataReader reader = myresult.cmd.EndExecuteReader(myresult.originalState as IAsyncResult)) 
     { 
      try 
      { 
       while (reader.Read()) 
       { 
        res.Add(new Experiment(reader)); 
       } 
      } 
      catch (Exception ex) 
      { 
       throw ex; 
      } 
      finally 
      { 
       // Closing the reader also closes the connection, because this reader was created using the CommandBehavior.CloseConnection value. 
       if (reader != null) 
       { 
        reader.Close(); 
       } 
      } 
     } 
     return res; 
    } 

BeginGetExperiments返回類SqlCommandAsyncResult實現在另外IAsyncResult接口持有後來訪問我SqlCommand參考。

public class SqlCommandAsyncResult : IAsyncResult 
{ 
    public SqlCommand cmd { get; private set; } 
    public IAsyncResult originalState { get; private set; } 

    public SqlCommandAsyncResult(SqlCommand cmd, AsyncCallback callback, object state) 
    { 
     this.cmd = cmd; 
     this.originalState = cmd.BeginExecuteReader(callback, 
      state, 
      System.Data.CommandBehavior.SequentialAccess | // doesn't load whole column into memory 
      System.Data.CommandBehavior.CloseConnection // close connection immediately after read 
      ); 
    } 

    public object AsyncState 
    { 
     get { return originalState.AsyncState; } 
    } 

    public WaitHandle AsyncWaitHandle 
    { 
     get { return originalState.AsyncWaitHandle; } 
    } 

    public bool CompletedSynchronously 
    { 
     get { return false; } 
    } 

    public bool IsCompleted 
    { 
     get { return AsyncWaitHandle.WaitOne(0); } 
    } 
} 

我面臨的困難是在EndGetExperiments方法。我不知道如何訪問SqlCommand致電EndExecuteReader(...)。 通常我會使用BeginExecutereader中的狀態對象來傳遞命令。但是，如果我這樣做，我會得到以下例外： 「IAsyncResult的狀態必須是傳遞給您的Begin調用的狀態參數。」

所以我嘗試使用IAsyncResult將SqlCommand傳遞給EndGetExperiments。這裏，我不明白的是，在EndGetExperiments中，可變結果是類型IAsyncResult或類型SqlCommandAsyncResult，具體取決於SqlCommandAsyncResult類中的CompletedSynchronously的值。 設置CompletedSynchronously = false使我的代碼失敗，因爲我不能訪問SqlCommand，而設置CompletedSynchronously = true代碼的作品就像一個魅力，但我有一種奇怪的感覺，可能會出現問題。

感謝任何幫助，指導和示例代碼如何使這個代碼工作，甚至更重要的是幫助我瞭解手頭的問題。

非常感謝。 Jan

Answer 1

今天WCF數據服務不支持服務器上的異步處理。請在此處投票/添加功能請求：http://data.uservoice.com/forums/72027-wcf-data-services-feature-suggestions/topics/72603-wcf-data-services-feature-suggestions

Answer 2

如果您使用的是C＃4.0。這可能更容易使用Task<T>來實現。 Task<T>將執行Func<T>其中T是返回值。您可以定義一個獲取Parent.Result的延續任務。我知道這個答案可能不是你要找的。但請考慮將此作爲替代方案。代碼將更清潔，易於維護並且易於調試（使用任務並行窗口，並行堆棧等）。