的SqlCommand（using語句/處置問題）

Question

看看下面的例子...

 Using cn As New SqlConnection(ConnectionString) 
      Try 
       Dim cmd As SqlCommand = New SqlCommand 
       With cmd 
        .Connection = cn 
        .Connection.Open() 
        .CommandText = "dbo.GetCustomerByID" 
        .CommandType = CommandType.StoredProcedure 
        .Parameters.Add("@CustomerID", SqlDbType.Int, 4) 
        .Parameters("@CustomerID").Value = CustomerID 
       End With 

       da = New SqlDataAdapter(cmd) 
       da.Fill(ds, "Customer") 
      Catch ex As Exception 

      End Try 
     End Using 

從我的研究，今天聽起來好像這基本上是好的，但在SqlCommand的沒有被處理掉。

問題 - >以下哪個例子是處理這個問題的最好方法？

實施例2 - 棄置手動

 Using cn As New SqlConnection(ConnectionString) 
      Try 
       Dim cmd As SqlCommand = New SqlCommand 
       With cmd 
        .Connection = cn 
        .Connection.Open() 
        .CommandText = "dbo.GetCustomerByID" 
        .CommandType = CommandType.StoredProcedure 
        .Parameters.Add("@CustomerID", SqlDbType.Int, 4) 
        .Parameters("@CustomerID").Value = CustomerID 
       End With 

       da = New SqlDataAdapter(cmd) 
       cmd.Dispose() 
       da.Fill(ds, "Customer") 
      Catch ex As Exception 

      End Try 
     End Using 

實施例3 - 自動設置與使用語句

 Using cn As New SqlConnection(ConnectionString) 
      Try 
       Using cmd As New SqlCommand 
        With cmd 
         .Connection = cn 
         .Connection.Open() 
         .CommandText = "dbo.GetCustomerByID" 
         .CommandType = CommandType.StoredProcedure 
         .Parameters.Add("@CustomerID", SqlDbType.Int, 4) 
         .Parameters("@CustomerID").Value = CustomerID 
        End With 

        da = New SqlDataAdapter(cmd) 
        da.Fill(ds, "Customer") 
       End Using 
      Catch ex As Exception 

      End Try 
     End Using 

實施例4 - 同實施例3，但所述的try/catch是使用內 - 這是否有所作爲？

 Using cn As New SqlConnection(ConnectionString) 
      Using cmd As New SqlCommand 
       Try 
        With cmd 
         .Connection = cn 
         .Connection.Open() 
         .CommandText = "dbo.GetCustomerByID" 
         .CommandType = CommandType.StoredProcedure 
         .Parameters.Add("@CustomerID", SqlDbType.Int, 4) 
         .Parameters("@CustomerID").Value = CustomerID 
        End With 

        da = New SqlDataAdapter(cmd) 
        da.Fill(ds, "Customer") 
       Catch ex As Exception 

       End Try 
      End Using 
     End Using 

示例5 - 與示例4相同，但在Using語句中指定了CommandText和cn - 它具有哪些優點？

 Using cn As New SqlConnection(ConnectionString) 
      Using cmd As New SqlCommand("GetCustomerByID", cn) 
       Try 
        With cmd 
         .Connection.Open() 
         .CommandType = CommandType.StoredProcedure 
         .Parameters.Add("@CustomerID", SqlDbType.Int, 4) 
         .Parameters("@CustomerID").Value = CustomerID 
        End With 

        da = New SqlDataAdapter(cmd) 
        da.Fill(ds, "Customer") 
       Catch ex As Exception 

       End Try 
      End Using 
     End Using 

示例6 - 與示例5相同，但連接在cn而不是cmd上打開。如果只有一個存儲過程被執行，在cmd上打開連接會更好嗎？

 Using cn As New SqlConnection(ConnectionString) 
      cn.Open() 

      Using cmd As New SqlCommand("GetCustomerByID", cn) 
       Try 
        With cmd 
         .Connection = cn 
         .CommandType = CommandType.StoredProcedure 
         .Parameters.Add("@CustomerID", SqlDbType.Int, 4) 
         .Parameters("@CustomerID").Value = CustomerID 
        End With 

        da = New SqlDataAdapter(cmd) 
        da.Fill(ds, "Customer") 
       Catch ex As Exception 

       End Try 
      End Using 
     End Using 

Answer 1

的DataAdapter.Fill方法命令將打開和關閉連接本身，所以你不需要cmd.Connection.Open()。 （參考：http://msdn.microsoft.com/en-us/library/377a8x4t.aspx中的備註部分。）

對於SqlConnection使用Using具有爲您調用.Close的效果。

變量cmd一旦超出範圍（或更早，如果.NET確定它不會再次使用），它就有資格進行垃圾回收。

在你的例子2中，我不確定在DataAdapter使用它之前處理cmd是個好主意。