CODEWITHSUNDEEP
c#entity-framework
mberube.Net
mberube.Net

Reputation: 2180

Behavior I can't explain with Entity Framework

I'm trying to find documentation about a behavior in Entity Framework. It works but before relying on this behavior, I want to be sure it's a normal behavior of EF and not a unexpected side effect that would be "fixed" in a future version. Here's the situation :

I've a pretty deep object hierachy (which I will simplify here). The structure is a multi levels collection of objects (class A contains a collection of class B which contains a collection of class C, which contains ...) for 7 levels deep.

I've to filter elements on some properties of C and my first trials of doing it loading the complete hierachy produce a complicated LINQ query (which would be a maintenance nightmare) and the generated SQL query was far from efficient. To simplify all this, I decided to split the query in 2 steps : first, I load the collection of class C (and all its childs) filtered as I want and then, I load class A and B for all instances of B that contains an item of my filtered collection of C.

Here's the catch : using that technique, I expected to have to repopulate manually the collection of C in my B class but actually, the collection is already populated with the elements of the collection. I verified the SQL query in intellitrace and the data required to fill instances of C is not included in the second query so the only logical conclusion is that EF did this from the informations in the context. BTW, lazy loading is turned off for that context.

Is this behavior normal in EF ? It so, can you give me link to the documentation explaining how this works ?

Here's a snippet to illustrate this :

using(var context = new MyContext())
{
    //Includes and where clauses are greatly simplified for the purpose of the sample
    var filteredC = context.C.Include(x=>x.ListOfD).Include(x=>x.ListOfD.Select(y=>y.ListOfE)).Where(c=>c.Status==Status).ToList();

    int[] bToLoad = filteredC.Select(c=>c.IDofB).Distinct().ToArray();

    var listOfAAndB = context.A.Include(a=>a.ListOfB).Where(x=>x.ListOfB.Any(y=>bToLoad.Contains(y.ID))).ToList();

    //At this step, I expected B.ListOfC to be empty but it's somehow populated
}

Thanks

Upvotes: 2

Views: 70

Answers (1)

H. Lowette
H. Lowette

Reputation: 324

This is standard behavior for a DbContext life cycle. To be honest, I can't link you to any documentation that documents this feature, but I can explain you how this works.

An EF Context is stateful, and keeps track of all the entities that have already been fetched. It also knows about the relations between entities in your DB and your entity model.

So if you fetch new objects that have a direct relation to that object (in your case, C has a foreign key to B), the navigation property is populated by the Context. This is a feature, and not a bug, as it tries to explicitly avoid Lazy loading queries to the DB for objects that have already been fetched.

Upvotes: 3

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