Friday, March 13, 2009

WCF auto generated client proxy classes - instantiation gotcha

WCF auto-generated client proxy classes all implement IDisposable. This makes them candidates for instantiating via using statements i.e.:

using (MyServiceBindingClient client = new MyServiceBindingClient())

This approach should not be taken when working with WCF client proxy classes. This is because if an exception is thrown within the try block above, you will never get to see the true exception:

The problem is that if the client.Open() call (or any subsequent calls placed on the client) throws an exception, we end up leaving the using block, which causes our client’s IDisposable interface to get fired. The Dispose routine on WCF classes have a bad tendency to then fire another exception at that point, because we are attempting to perform a close() operation on the client but it has already faulted. And so the exception that eventually gets caught by any surrounding try/catch block will be the exception thrown by calling close() on a faulted client. It will not be the original exception, and the original exception is not accessable via the InnerException property.

Microsoft’s recommended way of avoiding this situation is to not instantiate WCF clients via using statements. I.e. instantiate/use them as per non-IDisposable’s, and make sure you have appropriate exception handling and explicit calls to dispose your IDisposable.

Thursday, February 26, 2009

Back porting SQL Server 2005 to 2000


We had a SQL Server 2005 DotNetNuke database full of proprietary data that we needed to back-port to SQL Server 2000, due to a limitation on the eventual destination hosting site.

The Problem

SQL Server 2000 will not natively restore databases from backups made on SQL Server 2005, and will not attach SQL Server 2005 data/log files. So we needed to find an alternative way to move our data and schema objects from the SQL 2005 instance back to 2000. Something like Redgate, but perhaps a little cheaper and simpler if possible.

The Solution

Microsoft offers a free download called the SQL Server 2005 Database Publishing Wizard. This tool presents a wizard-style interface that allows you to script out your database in its entirety (all data and objects) into a single SQL script. This script can be targeted at either SQL Server 2000 or 2005.

With just a few mouse clicks we had generated a single SQL script that contained our entire database. The script ran up perfectly first time under SQL Server 2000, giving us the desired result of our DotNetNuke database being back-ported successfully to SQL Server 2000.

The tool can be found at: