Entity framework - “Problem in mapping fragments”-error. Help me understand the explanations of this error

Question

Error 3007: Problem in Mapping Fragments starting at lines 186, 205: Non-Primary-Key column(s) [WheelID] are being mapped

Answer 1

For LinQ to Entities queries in EF1, my workaround for not having access to the foreign key as a property is with the following code, which does not produce a join query to the associated table:

dbContext.Table1s.FirstOrDefault(c => (int?)c.Table2.Id == null)

i.e, the generated SQL is:

...WHERE ([Extent1].[Table2Id] IS NULL)...