Question

请参阅以下代码：

Private Sub TransactionExample3()
        Dim objDR As SqlDataReader
        Dim objCommand As SqlCommand, objCommand2 As SqlCommand
        Dim objCon As SqlConnection
        Dim objCon2 As SqlConnection
        Dim id As Integer
        Dim list As List(Of Integer) = New List(Of Integer)
        Try
            _ConString = "Data Source=databaseserver;Initial Catalog=Person;User ID=username;Password=password;MultipleActiveResultSets=True"
            list.Add(1)
            list.Add(2)
            list.Add(3)

            For Each i As Integer In list
                Using trans = New TransactionScope()
                    objCon2 = New SqlConnection(_ConString)
                    objCon2.Open()
                    objCommand2 = New SqlCommand()
                    objCommand2.Connection = objCon2
                    Using objCon2
                        objCommand2.CommandText = "UPDATE Person SET forenames = @forenames WHERE " & _
                            " Reference = @Reference "
                        objCommand2.Parameters.AddWithValue("@forenames", i + 1)
                        objCommand2.Parameters.AddWithValue("@Reference", i)
                        objCommand2.ExecuteNonQuery()
                        objCommand2.Parameters.Clear()
                    End Using
                    trans.Complete()
                End Using
            Next

        Catch ex As Exception
            Throw
        Finally

        End Try

    End Sub

此代码适用于每个循环，更改将提交到数据库。

现在请看下面的代码：

Private Sub TransactionExample3()
        Dim objDR As SqlDataReader
        Dim objCommand As SqlCommand, objCommand2 As SqlCommand
        Dim objCon As SqlConnection
        Dim objCon2 As SqlConnection
        Dim id As Integer
        Try
            _ConString = "Data Source=server;Initial Catalog=Person;User ID=Username;Password=Password;MultipleActiveResultSets=True"
            objCon = New SqlConnection(_ConString)
            objCommand = New SqlCommand("SELECT top 10 * from Person")
            objCommand.Connection = objCon
            objCon.Open()
            objDR = objCommand.ExecuteReader()
            Do While objDR.Read
                objCon2 = New SqlConnection(_ConString)
                objCon2.Open()
                Using trans = New TransactionScope()
                    objCommand2 = New SqlCommand()
                    objCommand2.Connection = objCon
                    Using objCon2
                        objCommand2.CommandText = "UPDATE Person SET forenames = @forenames WHERE " & _
                            " Reference = @Reference "
                        objCommand2.Parameters.AddWithValue("@forenames", objDR("Reference") + 10)
                        objCommand2.Parameters.AddWithValue("@Reference", objDR("Reference"))
                        objCommand2.ExecuteNonQuery()
                        objCommand2.Parameters.Clear()
                    End Using
                End Using
            Loop
            objDR.Close() 'line 16
        Catch ex As Exception
            Throw
        Finally

        End Try

    End Sub

在第二个代码exherpt中，范围不完整（scope.complete），但结果仍然在while循环的每次迭代时提交给数据库。这是为什么？

Answer 1

在第一个循环中，TransactionScope的打开位于连接打开之前。在第二个是后。该连接未在事务中登记，因此每个命令都在不由事务持有的情况下执行。

尝试切换这些行

Do While objDR.Read
    Using trans = New TransactionScope()
       objCon2 = New SqlConnection(_ConString)
       objCon2.Open()
       .....

现在您需要调用trans.Complete（）

Private Sub TransactionExample3()
    Dim objDR As SqlDataReader
    Dim objCommand As SqlCommand, objCommand2 As SqlCommand
    Dim objCon As SqlConnection
    Dim objCon2 As SqlConnection
    Dim id As Integer
    _ConString = "Data Source=server;Initial Catalog=Person;User ID=Username;Password=Password;MultipleActiveResultSets=True"
    Using objCon = New SqlConnection(_ConString)
        objCommand = New SqlCommand("SELECT top 10 * from Person")
        objCommand.Connection = objCon
        objCon.Open()
        objDR = objCommand.ExecuteReader()
        Using trans = New TransactionScope()
        Using objCon2 = New SqlConnection(_ConString)
            objCon2.Open()
            Do While objDR.Read
                objCommand2 = New SqlCommand()
                objCommand2.Connection = objCon
                Using objCon2
                    objCommand2.CommandText = "UPDATE Person SET forenames = @forenames WHERE " & _
                        " Reference = @Reference "
                    objCommand2.Parameters.AddWithValue("@forenames", objDR("Reference") + 10)
                    objCommand2.Parameters.AddWithValue("@Reference", objDR("Reference"))
                    objCommand2.ExecuteNonQuery()
                    objCommand2.Parameters.Clear()
                End Using
            Loop
            objDR.Close() 'line 16
        End Using
        trans.Complete()
        End Using    
    End Using
End Sub

我建议在循环之外移动事务和连接开头并调用Complete并在foreach循环之后销毁连接，如果我正确理解你的代码你在每个循环更新一条记录，那么只有你的事务才有意义想要更新所有记录或没有。另一个小的优化可能是在循环外移动SqlCommand和Parameters的创建。您只更新循环内的参数值，而不会在每个循环中销毁和重建参数集合

TransactionScope在每个循环上提交

1 个答案: