Paul Hiles Paul Hiles - 10 months ago 54
C# Question

How to declare one to one relationship using Entity Framework 4 Code First (POCO)

How to declare a one to one relationship using Entity Framework 4 Code First (POCO)?

I found this question (one-to-one relationships in Entity Framework 4) , but the article that the answer references was not useful (there is one line of code that is a 1-1 relationship, but no mention of how to define it).

Answer Source

Are you just looking for something like this?

public class User
    public int Id { get; set; }
    public string Username { get; set; }
    public Profile Profile { get; set; }
    public int ProfileId { get; set; }

public class Profile
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string PostalCode { get; set; }
    // etc...

public class UserMapping : EntityConfiguration<User>
    public UserMapping()
        this.HasKey(u => u.Id);
        this.Property(u => u.Username).HasMaxLength(32);

        // User has ONE profile.
        this.HasRequired(u => u.Profile);

public class ProfileMapping : EntityConfiguration<Profile>
    public ProfileMapping()
        this.HasKey(p => p.Id);
        this.Property(p => p.FirstName).HasMaxLength(32);
        this.Property(p => p.LastName).HasMaxLength(32);
        this.Property(p => p.PostalCode).HasMaxLength(6);

EDIT: Yeah I didn't have VS in front of me but you need to add the following line in the UserMapping instead of the current HasRequired and also add a ProfileId property (instead of Profile_Id that you added):

this.HasRequired(u => u.Profile).HasConstraint((u, p) => u.ProfileId == p.Id);

I currently don't think there's a way around this, but I'm sure it'll change since we're only in CTP4. It'd be nice if I could say:

this.HasRequired(u => u.Profile).WithSingle().Map(
    new StoreForeignKeyName("ProfileId"));

This way I wouldn't have to include a ProfileId property. Maybe there is a way around this currently and it's still to early in the morning for me to think :).

Also remember to call .Include("Profile") if you want to include a "navigational property".