title: The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations
body: <p><strong>"The principal end of this association must be explicitly configured using either the relationship fluent API or data annotations."</strong></p>
  
  <p>I am getting this error in Entity Framework 4.4 when updating/migrating the database, but I am not trying to specify a 1:1 relationship.  I want something like this:</p>
  
  <pre><code>public class EntityA
  {
      public int ID { get; set; }
      public int EntityBID { get; set; }
  
      [ForeignKey("EntityBID")]
      public virtual EntityB EntityB { get; set; }
  }
  
  public class EntityB
  {
      public int ID { get; set; }
      public Nullable&lt;int&gt; PreferredEntityAID { get; set; }
  
      [ForeignKey("PreferredEntityAID")]
      public virtual EntityA PreferredEntityA { get; set; }
  }
  </code></pre>
  
  <p>where EntityA must have an EntityB parent, whereas EntityB can have a preferred EntityA child, but doesn't have to.  The preferred child should be one of the children associated with the parent, but I don't know how to enforce this in the database.  I'm planning on enforcing it programmatically.    </p>
  
  <p>How do I get around this error or what is a better way of accomplishing these relationships?    </p>