I can't take this out because we use the ForeignKey field as the join field. So basically a column reference and a join reference in the same field. Doing 'foreignfield_id' > 5 maps you to 'foreignfield' > 5. This is symmetrical to what used to be in 'RelatedField.get_db_prep_lookup'. If you would like, I can raise an exception in the multicolumn case.