vb.net – SqlCommand(使用Statement / Disposing问题)

以下面的例子为例……

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

根据我今天的研究,听起来好像这基本上还可以,但是sqlCommand没有被处理掉.

问题 – >以下哪个例子是处理这个问题的最佳方法？

示例2 – 手动处理

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",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

示例3 – 使用Using语句自动处理

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",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

示例4 – 与示例3相同,但Try / Catch在使用中 – 这是否有所不同？

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","Customer")
                Catch ex As Exception

                End Try
            End Using
        End Using

示例5 – 与示例4相同,但CommandText和cn在Using语句中指定 – 这有什么优势？

Using cn As New sqlConnection(ConnectionString)
            Using cmd As New sqlCommand("GetCustomerByID",cn)
                Try
                    With cmd
                        .Connection.open()
                        .CommandType = CommandType.StoredProcedure
                        .Parameters.Add("@CustomerID","Customer")
                Catch ex As Exception

                End Try
            End Using
        End Using

示例6 – 与示例5相同,但是在cn而不是cmd上打开连接.如果只执行一个存储过程,是否最好在cmd上打开连接？

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","Customer")
                Catch ex As Exception

                End Try
            End Using
        End Using

DataAdapter.Fill命令将打开和关闭连接本身,因此您不需要cmd.Connection.open(). (参考： http://msdn.microsoft.com/en-us/library/377a8x4t.aspx的备注部分.)

使用Using for sqlConnection可以为你调用.Close.

变量cmd一旦超出范围就变得有资格进行垃圾收集(如果.NET确定它不会再次使用,则更早).

在你的例子2中,我不确定在DataAdapter使用它之前处理cmd是个好主意.