build_from

# File activerecord/lib/active_record/relation/query_methods.rb, line 1783
      def build_from
        opts = from_clause.value
        name = from_clause.name
        case opts
        when Relation
          if opts.eager_loading?
            opts = opts.send(:apply_join_dependency)
          end
          name ||= "subquery"
          opts.arel.as(name.to_s)
        else
          opts
        end
      end