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,在cmd上打开连接会更好吗?
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
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的评论部分。)
使用Using
进行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,则变得更早)。
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Should I call Dispose on a SQLCommand object?用户“JefBar软件服务”的信息]在撰写本文时,由于.Dispose
,在SqlCommand
上调用code in its constructor没有任何效果:
public SqlCommand() : base() {
GC.SuppressFinalize(this);
}