Question

我需要一些帮助才能正确实现强类型TableAdapters

的USING语句

我有这样的事情：

Using myDT As New mbr_Account.mbr_AccountDataTable
     Using myTA As New mbr_AccountTableAdapters.mbr_AccountTableAdapter
           myTA.Connection.Open()
           myTA.Fill(myDT)
           myTA.Connection.Close()
     End Using

     For Each row In myDT
          'do stuff
     Next
End Using

这将正确处理数据表和tableadapter，但不解决连接对象的问题。

我应该如何处置Connection对象？

我可以在Try中包装连接...最后像这样：

Using myDT As New mbr_Account.mbr_AccountDataTable
    Using myTA As New mbr_AccountTableAdapters.mbr_AccountTableAdapter
        Try
            myTA.Connection.Open()
            myTA.Fill(myDT)
        Finally
            If Not IsNothing(myTA.Connection) Then
                myTA.Connection.Close()
                myTA.Connection.Dispose()
            End If
        End Try
    End Using

    For Each row In myDT
        'do stuff
    Next
End Using

问题：如何使用USING关键字代替Try ..最后是连接对象？

Answer 1

你有什么理由不能使用DataReader吗？

Dim sql As String = "SELECT whatever FROM SomeTable"
Using myConnection As New SqlConnection(MyConnectionstring)
    Using myCommand As New SqlCommand(sql, myConnection)
        myConnection.Open()
        Using myReader As SqlDataReader = myCommand.ExecuteReader()
            Dim myTable As New DataTable()
            myTable.Load(myReader)
            myConnection.Close()
            Return myTable
        End Using
    End Using
End Using

连接将被关闭并自动处理。

Answer 2

我刚刚发现TableAdapters会自动处理连接的打开和关闭，无需手动添加代码。

基本上，它们已经包含Try ... Finally块来处理异常期间的连接关闭。

Designer生成的插入/删除/更新代码如下所示：

global::System.Data.ConnectionState previousConnectionState = this.Adapter.InsertCommand.Connection.State;
    if (((this.Adapter.InsertCommand.Connection.State & global::System.Data.ConnectionState.Open) 
                != global::System.Data.ConnectionState.Open)) {
        this.Adapter.InsertCommand.Connection.Open();
    }
    try {
        int returnValue = this.Adapter.InsertCommand.ExecuteNonQuery();
        return returnValue;
    }
    finally {
        if ((previousConnectionState == global::System.Data.ConnectionState.Closed)) {
            this.Adapter.InsertCommand.Connection.Close();
        }
    }

因此无需关闭或处置连接对象。

USING语句和TableAdapters连接

2 个答案: