Entity Framework - Load entities with child entity

Question

What I am trying is to load all the A entities in the database together with B entities. The relationship between them is Every A entitiy has one B entitiy.

The project I am working on has a repository pattern and it has an All() method as below.

 public class EFRepository<T> : IRepository<T> where T : class, IObjectWithChangeTracker { private IObjectSet<T> objectset; private IObjectSet<T> ObjectSet { get { if (objectset == null) { objectset = UnitOfWork.Context.GetObjectSet<T>(); } return objectset; } } public virtual IQueryable<T> All() { return ObjectSet.AsQueryable(); } }

Is there any way that I can force B entities to eager load. What I've found is there there is no Include method on the IQueryable that returns from the All() method. I am happy to add a new member to repositroy so it can allow the client to use eager loading. But how can I do it?

StriplingWarrior · Accepted Answer · 2011-09-27 15:35:21Z

The problem is that IQueryable is agnostic of what's backing it, and Include is an Entity Framework feature. You could have an IQueryable that uses LINQ to Objects instead, and Include wouldn't make sense there. The easiest thing would be to change the type of All() to an IObjectSet, from which you should have access to an Include extension method.

If you can't change the return type of All, you will have to structure your queries in such a way that they pull in the child elements eagerly.

IList<Parent> parentsWithEagerLoadedChildren = parentRepo.All() .Select(p => new {p, p.Children}).ToList() // EF will attach the children to each parent .Select(p => p.p).ToList(); // Now that everything is loaded, select just the parents

Thanks your example worked and I am happy to report that it is sending one single query to get all the entitiy As and their Bs, which I was not expecting.
Regarding IObjectSet, I couldn't access to an include method. Then I saw this stackoverflow.com/questions/2586351/… which might be a better way to solve it

Joel C · Accepted Answer · 2011-09-27 16:00:56Z

You can create your own extension method which will allow you to use Include(path) against any IQueryable<T>:

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

There's a full explanation on Julie Lerman's blog: http://thedatafarm.com/blog/data-access/agile-entity-framework-4-repository-part-5-iobjectset/

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