Creating relationships in CodeFirst EF which reference each other - entity-framework

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"));