Wednesday, February 03, 2010

Mocking Entity Framework ObjectSets

After finally getting my head around object-graph deletes in Entity Framework v4, I set about getting some better testing around my EF code.  The first step was updating my self-tracking entities template to have my object-sets be exposed as IObjectSets which involved a small tweak to my TT file.

I ran into some challenges using a Rhino Mock of IObjectSet, so I let Google do some work for me and I landed on Jamie Phillip’s post about mocking IObjectSet via his MockObjectSet., which was exactly what I was looking for.  Adding this class into my test library got me 90% of where I wanted to be, but I still had compile errors on the spots where I was building out my object-graphs with “.Include(“”)” calls. 

After some time digging through the EF4 code with Reflector,  I was not finding what I thought I needed, an IObjectQuery interface, which would allow me to mock the Include method.  Again, I went back to Google and ran across a MSDN Forum post which Diego Vega answered with an almost too obvious solution to my exact problem: use an extension-method for Include.

Since I was only interested in mocking out the “Include” behavior, and have my MockOjectSet return my configured entity list, I went with Diego’s first suggestion for Include, which looks like this:

public static IQueryable<T> Include<T>(this IQueryable<T> source, string path){
   var objectQuery = source as ObjectQuery<T>;
   if (objectQuery != null){
      return objectQuery.Include(path);
   return source;

The only pain point to this approach to testing, is that I’m stuck remembering that I need to add a new extension method whenever I utilize one of the methods in the ObjectQuery<T> class – Union, Distinct, etc.