About Part 4

Fourth part is about 10 min in length. Covers how to implement table per hierarchy inheritance model (TPH) with Entity Framework 4.0

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I think the proper way to start this post is to ask How do you do eager loading with Entity Framework? And the basic native simple answer is by using ObjectQuery<T>.Include(string) method. No matter what you tried to do, you’ll end up using this way.

So there was ideas about how enhance the eager loading in our Entity Framework base applications. You can read about some of these ideas:

• Entity Framework Include with Func & Entity Framework Include with Func next by Matthieu MEZIL
• Typed Eager Loading Using Entity Framework (& What is Eager Loading vs Deferred Loading) by Meligy
• Fetching strategy posts by Simon Segal:
• Fetching Strategies for the Entity Framework - a waste of time for now?
• Entity Framework Repository, Specifications and Fetching Strategies
• The Entity Framework and a unified Lazy and Eager loading framework
• Entity Framework, Repositories, Specifications and Fetching Strategies Part 9.0
• Lazy Loading and Fetching Strategies again, with feeling!
• Lazy Loading and the Entity Framework. How long I can go on like this?

As I said, no matter what you tried, you’ll end up using ObjectQuery<T>.Include(string).

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On part 1 and part 2 I explored how to apply 2 different inheritance models (TPH & TPT) in Entity Framework. In this part I'm going to demonstrate associations between 2 base entities. And how to filter end properties to return specific type (sub entity). Download the sample.

Review Association Ends:

In previous part when I added department tables to the entity model diagram, an associations between Person and Department entities was automatically defined. This relation actually demonstrate the relation between Administrator and Department. It is one-to-many relationship where one person can be administrator of one or many departments.

A collection of Departments is created on Person table and therefor it is inherited on all sub entities! But this make no sense, as a student or instructor has nothing to do with this collection. Beside on the other end at Department a property of type Person is created -I renamed it to Administrator-, while this shouldn't be just any Person, this Person must be of type Administrator.

A few modification should take place in here. The existing association should be deleted and the association ends should be define between Administrator Entity and Department Entity. To do that follow the following steps:

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