Question

I’m wondering if this is a good way of doing data access, in terms of all the database objects being properly closed and disposed? For example:

Using conn As New SqlConnection(MyConnectionString)
  Using cmd As New SqlCommand("some SQL here", conn)
    ... add parameters ...
    conn.Open()
    Using dr As SqlDataReader = cmd.ExecuteReader()
      While dr.Read()
        ... do stuff ...
      Wend
    End Using
  End Using
End Using

Is nesting Using like acceptable practice? If I exit the method at some point within the Read() loop, will the use of Using like this ensure all objects are cleaned up properly regardless?

Answer 1

Using guarantees orderly disposal in an implicit try/finally block.

' THE FOLLOWING TRY CONSTRUCTION IS EQUIVALENT TO THE USING BLOCK
Dim resource As New resourceType
Try 
    ' Insert code to work with resource.
Catch ex As Exception
    ' Insert code to process exception.
Finally 
    ' Insert code to do additional processing before disposing of resource.
    resource.Dispose() 
End Try 

Nested usings work in a similar fashion. If you exit a block of code, it will execute the finally block, and properly dispose your objects.

http://msdn.microsoft.com/en-US/library/htd05whh(v=VS.80).aspx