construct_relation_for_association_calculations

# File activerecord/lib/active_record/relation/finder_methods.rb, line 379
    def construct_relation_for_association_calculations
      from = arel.froms.first
      if Arel::Table === from
        apply_join_dependency(self, construct_join_dependency)
      else
        # FIXME: as far as I can tell, `from` will always be an Arel::Table.
        # There are no tests that test this branch, but presumably it's
        # possible for `from` to be a list?
        apply_join_dependency(self, construct_join_dependency(from))
      end
    end