Inserted navigation property does not load

Question

I've a class:

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int UserId { get; set; }
    public virtual User User { get; set; }
}

In the User Table:

Id    Name    
1     Tommy
2     John

I create an object:

Person P = new Person { Name = "Test", UserId = 1 };

I insert the Person object into the database:

db.Persons.Add(P);
db.SaveChanges();
var user = P.User;

The problem is if I try to access P.User it contains null. Other properties of P are populated properly.

Why?

Did you set user? It looks like you create a Person but don't associate the person with a user - is the UserId supposed to do that? You've also got a lazy loaded (virtual) nav property, it might be worth profiling the SQL server to see what it tries to load when you access the property — Charleh, Nov 06 '13 at 18:00
possible duplicate of [Entity Framework: I set the foreign key, SaveChanges then access the navigation property, but it doesn't load the related entity. Why not?](http://stackoverflow.com/questions/15552891/entity-framework-i-set-the-foreign-key-savechanges-then-access-the-navigation) — Colin, Nov 07 '13 at 10:09
And the solution I now use with the repository pattern: http://stackoverflow.com/questions/16736143/how-to-ensure-proxies-are-created-when-using-the-repository-pattern-with-entity — Colin, Nov 07 '13 at 10:10

score 2 · Answer 1 · answered Nov 06 '13 at 23:11

2

You should create the Person as follows:

Person p = db.Persons.Create();
p.Name = "Test";
p.UserId = 1;

The difference is that the Person is now created as a dynamic proxy, which means that it is capable of lazy loading. Once it is attached to the context (by db.Persons.Add) you can access the associated User.

answered Nov 06 '13 at 23:11

Gert Arnold

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I'm using repository & unit of work pattern, could you tell me how I can incorporate this? – hendrixchord Nov 07 '13 at 04:06
Where have you got the `new Person` call now? It should be possible to replace that, I guess, since the repo should have a `DbContext` or a `DbSet`. – Gert Arnold Nov 07 '13 at 08:00

score 0 · Answer 2 · answered Nov 06 '13 at 18:02

You should mark the UserId property as a foreign key like:

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    [ForeignKey("User")]
    public int UserId { get; set; }
    public virtual User User { get; set; }
}

Like that, the entity framework will know that your UserId property is supposed to belong to the User property.

score 0 · Answer 3 · answered Nov 06 '13 at 18:10

I think you need to execute a new query for the person. An Entity Framework insert query will only return the id of the new object by using SCOPE_IDENTITY(), so the related objects aren't loaded. What if you do this:

var newPerson = db.Persons.Find(P.Id);
var user = newPerson.User;

Inserted navigation property does not load

3 Answers3