接下来是一个例子...
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
根据我的研究,今天看起来基本上是可以的,但SqlCommand没有被处理。
问题->以下哪个示例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", 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语句自动释放资源
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位于Using内部 - 这会有所不同吗?
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 - 这样做有什么优势?
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,但连接是在cn上打开而不是cmd。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