EF Code First：包括不处理可选关系

Question

I have a specific query in my code which needs to eager load all related entities (both ->1 FKs and ->N FKs) because the context will be disposed right after that.

I made a generic "Query" method that takes params Expression<Func<MyItem, object>>[] includes and then internally chains them. That part works fine.

The query looks like this:

var item = facade.Query<MyItem>(
                c => c.Childs.Select(x => x.Parent),
                c => c.Childs.Select(x => x.SubChild1),
                c => c.Childs.Select(x => x.SubChildNotWorking),
                c => c.Childs.Select(x => x.SubChild2),
                c => c.Childs.Select(x => x.SubChild3),
                c => c.Childs.Select(x => x.SubChildrens)
                ).FirstOrDefault(c => c.Name == name);

The mapping for the not working property (placed in the configuration of SubChildNotWorking):

this.HasMany(scnw => scnw.Childs).WithOptional(c => c.SubChildNotWorking).HasForeignKey(c => c.MyForeignKey);

Of all the includes, only the SubChildNotWorking doesn't actually work. When inspecting with the debugger the returned object, I see the proxies on all the properties. Opening the proxies gives me the correct data for all other relations, and a "The objectcontext has already been disposed exception" for the SubChildNotWorking property.

The only difference I was able to spot is that the SubChildNotWorking is a nullable FK (with nullable column on the DB and WithOptional configuration in the dbcontext) while all the others are non nullable FKs configured with WithRequired.

The database also is a legacy DB not created with Code First and not following its conventions, I just made the mappings in the DbContext. Everything else works fine.

I am trying to figure out if eager loading doesn't work on nullable FKs but I couldn't find any documentation about that.

Is that a bug, or intended behavior? But most of all, how do I solve this?

Thanks.

Answer 1

Did you define

[DataContract]

on your class (entities)? If so, don't forget to annotate your SubChild with

[DataMember] 

or it might end up loaded but not showing up when you perform your GET call on entities.

Answer 2

When you are working with the include method, you are talking about the eager load pattern. Entities with relationship will be loaded as collections. For any not-nullable foreign key, there's a trivial collection starting empty, but for nullable ones, there is not. On the Code First you could make the navigation property virtual, but it's not your case. You can try load it directly on Context, for example:

var someEntity = context.someEntities.Find(1);
context.Entry(someEntity ).Reference(e => e.EntityWithFKNullable).Load(); 

or the shorter version:

context.EntitiesWithFKNullable.Load();