EF 4.1 - Add items to collection property that is virtual

Question

I'm using EF 4.1 code first. Given the following class snippet:

public class Doctor
{
    public virtual ICollection<Hospital> Hospitals { get; set; }
}

Note: I have this in the database context:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    this.Configuration.LazyLoadingEnabled = false;
}

I wanted to make sure that lazy loading is not involved here.

The issue I have is that, without the virtual keyword on the Hospitals property, when I retrieve a doctor that does have a hospital associated with him, the collection is empty. By including the virtual keyword, the hospitals collection does contain 1 item, which is what I expect.

The problem is that, when I want to create a brand new doctor and associate him with a hospital immediately, I get a Null reference exception, since the Hospitals property has not been initialised yet.

Can someone point out what I'm doing wrong here? How can I add items to the Hospitals upon creating a new doctor.

Cheers. Jas.

Answer 1

Your code is something what you usually see in all examples but to make this work this one is much better:

public class Doctor
{
    private ICollection<Hospital> _hospitals;
    public virtual ICollection<Hospital> Hospitals 
    { 
        get { return _hospitals ?? (_hospitals = new HashSet<Hospital>()); }
        set { _hospitals = value } 
    }
}

If you don't use virtual keyword EF will not initialize collection for you. In the same time if you create brand new Doctor via its constructor you must handle initialization yourselves.

Answer 2

I think this can help you.

public class Doctor
{
    public Doctor()
    {
       Hospitals = new ICollection<Hospital>();
    }

    public virtual ICollection<Hospital> Hospitals { get; set; }
}