Question

Does EF 4 support unidirectional one-to-many associations, as in:

public class Parent
{
  public int Id { get; set; }
  public string Something { get; set; }
  public List<Child> AllMyChildren { get; set; }
}

public class Child
{
  public int Id { get; set; }
  public string Anotherthing { get; set; }
  // I don't want a back-reference to the Parent!
  // public int ParentId { get; set; }
}

When I try to compile my project with an association between Parent and Child where End2 Navigation is blank (because I unchecked the End2 Navigation Property checkbox in the Add Association dialog), I get

Error 2027: No mapping specified for the following EntitySet/AssociationSet – Child.

UPDATE:

And what if I just have a List or similar property on Parent rather than a List? Do I need to create a wrapping type to hold the String so that I can also hold a back-reference to Parent?

Answer 1

Belive that this would work using Fluent API (Only way of deifning unidirectional associations)

modelBuilder.Entity<Child>()
.HasKey(t => t.Id);

modelBuilder.Entity<Parent>()
.HasMany(p => p.AllMyChildren)
.WithRequiredPrincipal();

http://msdn.microsoft.com/en-us/library/hh295843(v=VS.103).aspx