SPMetal, lookups without EntityRef

Question

I defined site definition with two content types and two list definitions. I have lookup site column

<Field ID="{4318c52f-11c6-129a-b832-5ab22450b17c}"
         Type="Lookup"
         List="Lists/Questions"
         ShowField="ID"
         Name="QuestionID"
         DisplayName="QuestionID"
         StaticName="QuestionID"
         Group="KnowledgeBase"
         DisplaceOnUpgrade="TRUE"
         Required="TRUE"/>

Than I use this field in Content Type

<ContentType ID="0x0100c2644b24e4ec4626be41a720171942a6"
               Name="CTAnswer"
               Group="Answer Content Type"
               Description="Answer Conent Type"
               Inherits="TRUE"
               Version="0">
    <FieldRefs>
      <FieldRef ID="{fa542e0f-0a70-4ab9-b92c-0177e6ddd247}" Name="AnswerContent"  
                DisplayName="Content"/>
      <FieldRef ID="{1318c52f-11c6-4b3a-b802-d0b22450b1bc}" Name="AnswerRank"   
                DisplayName="Rank"/>
      <FieldRef ID="{4318c52f-11c6-129a-b832-5ab22450b17c}" Name="QuestionID" 
                DisplayName="QuestionID"/>
    </FieldRefs>
  </ContentType>

and after that I create List Definition based on this content type. Everything is ok, but SPMetal generates my lookups as System.Nullable, and not as EntityRef. What is wrong? Where am I mistaken?

Answer 1

Both source and target list must be included in the generated classes, and fields of a type understood by SPMetal (no custom types).

If you really can't get them to generate, you can code them yourself in partial classes.