EF Code First not returning related objects

Question

I'm using EF Code First with a pre-existing database.

Two objects:

public Foo
{
    public int FooId {get;set;}
}

public Bar
{
    public int BarId {get;set;}
    public virtual Foo Foo {get;set;}
}

Both FooId and BarId are primary keys in the database, and the Bar table has a column FooId which is a foreign key pointing at the Foo table.

When I select a Bar, Foo is a null reference. I would have thought EF would have automatically pulled the two of them together, but perhaps I'm missing something?

Database mappings:

public class EFCodeFirst : DbContext
{
    public EFCodeFirst()
    {
        this.Database.Connection.ConnectionString = ConfigurationManager.ConnectionStrings["AlternateString"].ConnectionString;
    }

    public DBSet<Foo> Foos {get;set;}
    public DBSet<Bar> Bars {get;set;}

    protected override void OnModelCreating(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder)
    {
        modelBuilder.IncludeMetadataInDatabase = false;
        modelBuilder.Entity<Foo>().MapSingleType().ToTable("Foo");
        modelBuilder.Entity<Bar>().MapSingleType().ToTable("Bar");
    }
}

Answer 1

If your expectation of Foo should not be null is coming from the fact that you make it virtual on Bar object, then that's not the case. By make them virtual, you just opt in to EF lazy loading and it will be null up until to the point that you explicitly ask for it by accessing it on Bar object. Other than that, if you want it to be populated upfront you would have to eager load it with Include method.

To explicitly disable lazy loading you can use the following code, even though you don't need it since you can just remove the virtual keyword from your navigation properties and lazy loading would be gone.

public EFCodeFirst()
{        
    this.ObjectContext.ContextOptions.LazyLoadingEnabled = false;
}

Internally, DbContext uses a protected ObjectContext that you can also use inside your inherited DbContext class (e.g. EFCodeFirst).

Answer 2

You are missing a line in the Foo class, that Foo contains a collection of Bar.