entity framework code first double one to one relationship

Question

class Event{  
    int? EventID{get;set;}  
    int? FirstParticipantID{get;set;}  
    Participant FirstParticipant{get;set;}  
    int? SecondParticipantID{get;set;}  
    Participant SecondParticipant{get;set;}  
    int? CreatedByID{get;set;}  
    User CreatedBy{get;set;}  
}


class Participant{  
    int? ParticipantID{get;set;}  
    List<Event> Events{get;set;}  
    int? CreatedByID{get;set;}  
    User CreatedBy{get;set;}  
}

protected override void OnModelCreating(DbModelBuilder modelBuilder){  
    modelBuilder.Entity<Event>().HasRequired(m => m.FirstParticipant).WithMany(m => m.Events).HasForeignKey(m => m.FirstParticipantID);  
    modelBuilder.Entity<Event>().HasRequired(m => m.SecondParticipant).WithMany(m => m.Events).HasForeignKey(m => m.SecondParticipantID);  
    modelBuilder.Entity<Event>().HasRequired(m => m.CreatedBy);  
    modelBuilder.Entity<Participant>().HasRequired(m => m.CreatedBy);  
}

It seems very clear to me, but EF (and sql) keeps complaining, no matter what moves I make to the hasmanny/hasrequired stuff. I can't even find google help cause I don't know the name of what I'm trying to implement (double one to one???!!!)

The idea is that an Event must have 2 not null Participants (first & second only, not many) and that each Participant may have many Events

Thanks

Answer 1

There are multiple problems in your code:

• PK cannot be nullable
• FK cannot be nullable if you want to define the relation as Required
• When you define two relations with Participant you need two navigation properties - you cannot map two relations into single Events property
• You didn't complete your mapping of CreatedBy in both Event and Participant

Try this:

public class Event{  
    public int EventID {get;set;}  
    public int FirstParticipantID{get;set;}  
    public Participant FirstParticipant{get;set;}  
    public int SecondParticipantID{get;set;}  
    public Participant SecondParticipant{get;set;}  
    public int CreatedByID{get;set;}  
    public User CreatedBy{get;set;}  
}


public class Participant{  
    public int ParticipantID {get;set;}   
    public int CreatedByID {get;set;}  
    public User CreatedBy {get;set;}  
    public ICollection<Event> FristEvents { get; set; }
    public ICollection<Event> SecondEvents { get; set; }
}

protected override void OnModelCreating(DbModelBuilder modelBuilder){  
    modelBuilder.Entity<Event>()
                .HasRequired(m => m.FirstParticipant)
                .WithMany(m => m.FirstEvents)
                .HasForeignKey(m => m.FirstParticipantID);  
    modelBuilder.Entity<Event>()
                .HasRequired(m => m.SecondParticipant)
                .WithMany(m => m.SecondEvents)
                .HasForeignKey(m => m.SecondParticipantID);  
    modelBuilder.Entity<Event>()
                .HasRequired(m => m.CreatedBy)
                .WithMany()
                .HasForeignKey(m => m.CreatedByID);
    modelBuilder.Entity<Participant>()
                .HasRequired(m => m.CreatedBy)
                .WithMany()
                .HasForeignKey(m => m.CreatedByID);  
}