Question

I have some sample webservice like below,

<WebMethod()> _
    Public Function ExecuteCMD() As Boolean

        Dim cnn As New Data.SqlClient.SqlConnection        

        Try
        cnn.ConnectionString = "ConnectionString Here"
        cnn.Open()

        Dim cmd As New Data.SqlClient.SqlCommand("CommandText Here", cn)
        cmd.ExecuteNonQuery()

        Return True
        Catch ex As Exception
            Return False
        End Try
    End Function

Normally,we always close the connection after using it,
but there has never call close method.
Some of my friends said that
webservice is stateless method and it doesn’t matter
whether we have
close it or not.Is it true?I also know that cnn object life time is in
only that method and visualstudio will dispose it end of that method.
I really want to know object lifetime,how they allocated on memory and
when they are disposed after using.

Best Regards,
Chong

Answer 1

It does matter if you close the connection or not. SQL Server is quite resilient against lingering unclosed connections, but if you for example used Access you would quickly run out of available connections and get an error message when you tried to connect.

You have a connection object and a command object which both are disposable, so you should dispose them. Letting them go out of scope is not enough, the .NET memory management doesn’t work that way. The IDisposable interface is intended for objects with unmanaged resources that need to be cleared up.

Most disposable objects has a finaliser as fallback if you fail to dispose them, so they will be cleaned up eventually, but you want to aviod that. You want to dispose the objects as soon as possible, otherwise they will remain in memory until the garbage collector comes around to clean them up.

A Using block around the code where a disposable object is used is a good way to make sure that it’s disposed properly. It uses a Try...Finally block to ensure that the object is always disposed even if an error occurs.

<WebMethod()> _
Public Function ExecuteCMD() As Boolean

  Using connection As New Data.SqlClient.SqlConnection        

    Try
      connection.ConnectionString = "ConnectionString Here"
      connection.Open()

      Using command As New Data.SqlClient.SqlCommand("CommandText Here", connection)
        command.ExecuteNonQuery()
      End Using

      Return True
    Catch ex As Exception
        Return False
    End Try

  End Using

End Function