title: Entity framework with inheritance, condition, and foreign key
body: <p>I just started to play around with Linq to entities and ran into an issue I can't figure out. </p>
  
  <p>I am getting this error:  </p>
  
  <blockquote>
    <p>Condition member 'RelatedResources.TypeID' with a condition other than 'IsNull=False' is mapped. Either remove the condition on RelatedResources.TypeID or remove it from the mapping.</p>
  </blockquote>
  
  <p>The condition that exists is a TypeID field in the abstract entity RelatedResource that defines the type of RelatedResource (Book, Link, guide, etc.).  TypeID is also a foreign key and is mapped in the association with the Resource Type entity.  I think this is the problem but I don't know how or why I should change this.</p>