SqlCommand(使用Statement/Disposing问题)

Question

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此问题的最佳方法？

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", 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

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", 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

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", 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 - 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", 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 - 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", 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

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中的备注部分.)

使用Using了具有SqlConnection的调用的效果.Close就可以了你.

cmd一旦变量超出范围,变量就有资格进行垃圾收集(如果.NET确定它不会再次使用,则变量更早).

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.

[来自用户"JefBar Software Services"的信息我应该在SQLCommand对象上调用Dispose吗？]在编写本文时,由于其构造函数中的代码,调用.Disposean SqlCommand无效:

public SqlCommand() : base() {
    GC.SuppressFinalize(this);
}