与Code First的单向一对多关系

Question

I have a one-to-many uni-directional relationship between Contact and Phone defined like this:

class Contact {
    int ContactId {get; set}
    ICollection<Phone> Phones {get; set}
}
class Phone {
    int PhoneId {get; set;}
    string PhoneNumber {get; set;}
}

Now in the domain layer, i try to do the following:

someContact.Phones.Remove(somePhone);

and when i try to call context.SaveChanges() i get an exception because the relationship is defined as Required (eg. a phone cannot exist without a contact).
How can i solve this without using a foreign key or a navigation property in Phone and without the need to call DbSet<Phone>.Remove(Phone) before calling SaveChanges() ?

Answer 1

You basically answered your own question, as the two things you describe are separate:

1. Unlinking the object
2. Deleting the object

There may be a clever way for EF to do this, but others have asked the same question and been presented with the answer you alluded to:

eg EF 4.1: Removing child object from collection does not delete it - why?

Answer 2

There is a way to do both stapes that Matthew described in the single step. It requires a little change in your model - you have to add foreign key to the Phone entity and create a composite key that contains both PhoneId and ContactId .

This makes the instance of the Phone class tied to the instance of Contact class. With these settings, when you remove a phone from the contact someContact.Phones.Remove(somePhone); , EF removes phone from DB, because it knows that the phone can't exists without connection to that particular contact.

Models:

public class Contact {
    public int ContactId { get; set; }
    public virtual ICollection<Phone> Phones { get; set; }
}

public class Phone {
    public int PhoneId { get; set; }
    public int ContactId { get; set; }
    public string PhoneNumber { get; set; }
}

Configuration:

modelBuilder.Entity<Contact>()
    .HasMany(o => o.Phones)
    .WithRequired()
    .HasForeignKey(f => f.ContactId)
    .WillCascadeOnDelete(true);

modelBuilder.Entity<Phone>()
    .HasKey(o => new { o.PhoneId, o.ContactId });