Question

Say I have two DbContext, one containing breeds and one containing dogs.

public class Dog {
    public Breed Breed { get; set; }
    public Guid Id { get; set; }
    public string Name { get; set; }
}

public class Breed {
    public Guid Id { get; set; }
    public string Name { get; set; }
}

public class MainUnitOfWork : DbContext
{
    public MainUnitOfWork(): base("MainDb") { }
    public IDbSet<Breed> Breeds { get; set; }
}

public class NextUnitOfWork : DbContext
{
    public NextUnitOfWork() : base("NextDb") { }
    public IDbSet<Dog> Dogs { get; set; }
}

Now I try to insert a new dog.

var next = new NextUnitOfWork();

var dog = new Dog
    { Id = Guid.NewGuid(), Name = "Fido", 
      Breed = new Breed { Id = Guid.NewGuid(), Name = "Rotweiler" } };

next.Dogs.Add(dog);
next.SaveChanges();

Now I get two tables in NextDb, one for Dogs and one for Breeds. I hoped EF would figure out that the Breed really belonged to the MainDb since it’s declared in the MainUnitOfWork. Well, how do I proceed to bend EF to do what I want?

Answer 1

Even if EF would find a way to do it, it would be impossible to represent that in a relational database because there is no way to define a foreign key to a table in another database. At least not in mainstream relational database servers.

Dog table needs a foreign key to Breed to represent the many-to-one relationship.