Entity framework null reference on foreign key object

Question

I'm using Entity Framework Code First v 4.3.0

I have a two entities with a one to many relationship

e.g.

  public class User
  {
    [Key]
    public virtual string Username { get; set; }

    public virtual ICollection<Vacation> Vacations { get; set; }
  }

  public class Vacation
  {
    public int Id { get; set; }

    public virtual User User { get; set; }

    public virtual string UserUsername { get; set; }

  }

So the scenario is a User is created with a username of "User1". Subsequently a Vacation is created with the UserUsername field set to "User1". So we have our relationship.

If I then query the database after the Vacation is saved for the new Vacation User is null.

If I dispose of the DbContext and new it up. Requery for the Vacation User is set.

Any ideas why this might be?

What happens if you mark your User property in Vacation entity with [ForeignKey("UserUsername")]? — Ladislav Mrnka
– Ladislav Mrnka, Commented Mar 18, 2012 at 22:03
@LadislavMrnka I've done the mapping by overriding OnModelCreating method of dbContext — Tom Miller
– Tom Miller, Commented Mar 18, 2012 at 22:12
I have worked this out and will post answer in 6 hours due to rep. — Tom Miller
– Tom Miller, Commented Mar 18, 2012 at 22:15

Tom Miller · Accepted Answer · 2012-03-27 08:22:30Z

2

OK let me try and explain what the problem was.

Microsoft say that If lazy loading is enabled and a related entity is already loaded, it won't be loaded again.

I assume it's this design that is causing me problems.

I create my new Vacation, set UserUsername to "User1" and hit save. I then query the DbContext for the new vacation. Since this entity is already loaded within the context of my DbContext it isn't reloaded hence why User is null.

If I created a new DbContext and ran the same query User is populated.

I hope this makes sense.

answered Mar 27, 2012 at 8:22

Tom Miller

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1 Comment

Haikal Nashuha Over a year ago

can you please show me the example. I face this problem as well

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