Question

I am looking into migrate a large project to Entity Framework 4.0 but am not sure if it can handle my inheritance scenario.

I have several projects that inherit from an object in the “main” project. Here is a sample base class:

 namespace People
{
    public class Person
    {
        public int age { get; set; }
        public String firstName { get; set; }
        public String lastName { get; set; }

    }
}

and one of the sub-classes:

namespace People.LawEnforcement
{
    public class PoliceOfficer : People.Person
    {
        public string badgeNumber { get; set; }
        public string precinct { get; set; }
    }
}

And this is what the project layout looks like:

People – People.Education – People.LawEnforcement http://img51.imageshack.us/img51/7293/efdemo.png

Some customers of the application will use classes from the People.LawEnforcement and other users will use People.Education and some will use both. I only ship the assembles that the users will need. So the Assembles act somewhat like plug-ins in that they add features to the core app.

Is there anyway in Entity Framework to support this scenario?

Based on this SO question I’m think something like this might work:

ctx.MetadataWorkspace.LoadFromAssembly(typeof(PoliceOfficer).Assembly);

But even if that works then it seams as if my EDMX file will need to know about all the projects. I would rather have each project contain the metadata for the classes in that project but I’m not sure if that is possible.

If this isn’t possible with entity framework is there another solution (NHibernate, Active Record, etc.) that would work?

Answer 1

Yes this is possible, using the LoadFromAssembly(..) method you’ve already found.

… but it will only work if you have an specialized model (i.e. EDMX) for each distinct type of client application.

This is because EF (and most other ORMs) require a class for each entity in the model, so if some clients don’t know about some classes, you will need a model without the corresponding entities — i.e. a customized EDMX for each scenario.

To make it easier to create a new model for each client application, if I was you I’d use Code-Only following the best practices laid out on my blog, to make it easy to grab only the fragments of the model you need actually need.

Hope this helps

Alex