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