Entity Framework and avoiding the Anemic Domain Model

Question

In our business logic we occasionally have methods defined something like this:

User.ResetCourse(Course courseToReset)

The problem is that both User and Course are Entity Framework proxy objects. This means that when we hit navigation properties on either User or Course it can cause a huge hit to the database because those objects are not IQueryable so it iterates through them normally.

To solve this we changed the signature to:

User.ResetCourse(MyDBContext db, Course courseToReset)

This means we can directly query the database to make the changes we need in an efficient manner but passing the Database context to a business object just seems so wrong.

We later migrated to user a service layer which means we have something like:

CourseService.ResetForUser(Course courseToReset, User forUser)

This service has a reference to the DBContext injected in on creation but now our business objects are just data bags with no behaviour (i.e an Anemic Domain Model).

How can we avoid this?

Answer 1

The issue is, you are using EF objects as domain objects in the first place. EF objects are data models NOT business models.

You need to declare business objects which give you the freedom to do as you need, and then retrieve and store them with a repository. Your repository will map the EF entities to your business entities. EF objects should never be used outside of your repositories.

Answer 2

You can probably avoid it by doing something like:

CourseService.prepareForUserCourseReset(DBContext db);
User.reset();
Course.reset();
CourseService.completeUserCourseReset(DBContext db);

Or something to that effect, anyway, if you catch my drift. It sounds like the approach that you have with the initial way that you described is performance related, and not necessarily related to the structure of the domain. So really you should consider solving the performance issue in the service layer but can keep the behavior in the domain. It would be helpful to know what it means to reset the User / Course in this context as well if you want a better answer.

Answer 3

Traditionally, this is solved by using a fetching strategy for each use case that instructs Entity Framework to eager load the necessary associations on the initial query using IQueryable.Include().

Udi Dahan wrote a post that describes the general approach, which can be adapted to Entity Framework.

http://udidahan.com/2007/09/16/fetching-strategy-nhibernate-implementation-available/