Entity Framework - Error: define the key for entity type

Hallo everybody,

i have the following simple models.

public class A
{
    public B B { get; set; }
    public C C { get; set; }

}

public class B
{
    public i开发者_C百科nt Id { get; set; }


}

public class C
{
    public int Id { get; set; }

}

I get an error while i am trying to get the data:

System.Data.Edm.EdmEntityType: : EntityType 'A' has no key defined. Define the key for this EntityType.

Previous it was done via "RelatedTo". Has anybody a solution for this problem with the help of an example?

Thanks in advance!

Each entity in EF must have a primary key. It looks like A is junction table for many to many so you have multiple choices.

Remove A totaly and let EF handle many-to-many:

public class B
{
    public int Id { get; set; }
    public virtual ICollection<C> Cs { get; set; }
}

public class C
{
    public int Id { get; set; }
    public virtual ICollection<B> Bs { get; set; }
}

If you want A as entity you must either define additional key:

public class A
{
    public int Id { get; set; }
    public B B { get; set; }
    public C C { get; set; }
}

or you must include FK properties for B and C and mark them both as composite primary key (should be in db as well):

public class A
{
    public int bId { get; set; }
    public int cId { get; set; }
    public B B { get; set; }
    public C C { get; set; }
}

Edit:

Mapping for the last solution

modelBuilder.Entity<A>.HasKey(a => new { a.bId, a.cId });
modelBuilder.Entity<A>.HasRequired(a => a.B)
                      .WithMany()
                      .HasForeignKey(a => a.bId);
modelBuilder.Entity<A>.HasRequired(a => a.C)
                      .WithMany()
                      .HasForeignKey(a => a.cId);

Anyway if your A looks exactly as you described without any other properties you are definitely doing it wrong. Mapping A is only needed when it contains anything else then navigation properties / FKs for modelling many-to-many relation.