preloaders_for_hash

# File activerecord/lib/active_record/associations/preloader.rb, line 114
      def preloaders_for_hash(association, records, scope)
        association.flat_map { |parent, child|
          loaders = preloaders_for_one parent, records, scope

          recs = loaders.flat_map(&:preloaded_records).uniq
          loaders.concat Array.wrap(child).flat_map { |assoc|
            preloaders_on assoc, recs, scope
          }
          loaders
        }
      end