Creating relationships in CodeFirst EF which reference each other

Question

I having some issues setting up the correct relationships that I require for a database.

In words... I want to have a Firm which can multiple (zero:many) Branch

On the Firm I want to be able specify a HeadOffice which will exist will exist in the Branch table (zero:one)

What I expected to see is the Firm table to have the following fields: Id, Name, HeadOfficeId and on the Branches I expect to see: Id, TradingAs, Name, Firm_Id

Instead I see:

Firm table to have the following fields: Id, Name, HeadOfficeId

Branches I expect to see: Id, TradingAs, Name, Firm_Id, Firm_Id1

The model classes are as shown

public class Firm
{
    public int Id { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Branch> FirmBranches { get; set; }

    public virtual LawFirmBranch HeadOffice { get; set; }
}

public class Branch
{
    public int Id { get; set; }
    public string TradingAs {get;set;}
    public string Name {get;set;}


    public Firm Firm { get; set; }

}

I understand that this causes a circular reference type issue and I am happy to have the Firm HeadOffice to initially to be Null until there are values in the FirmBranches property.

Is there some way that I can specify that the HeadOffice has the null or one type relationship

Answer 1

If you're wanting to explicitly do this in your model, you can do this via data annotations:

public class Firm { public int Id { get; set; } public string Name { get; set; }

public virtual ICollection<Branch> FirmBranches { get; set; }

[ForeignKey("HeadOffice")]
public int? FirmId {get;set;}

public virtual LawFirmBranch HeadOffice { get; set; }

}

If you dont want this exposed in your code, you'll need to do this via fluent:

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Firm>()
            .HasOptional(f => f.HeadOffice)
            .WithOptionalDependent();
    }

This creates:

If you want to change the name of the key, you'd add a mapping to the end of the fluent map:

        modelBuilder.Entity<Firm>()
            .HasOptional(f => f.HeadOffice)
            .WithOptionalDependent()
            .Map(m => m.MapKey("YourKeyName"));