build_left_outer_joins

# File activerecord/lib/active_record/relation/query_methods.rb, line 978
      def build_left_outer_joins(manager, outer_joins, aliases)
        buckets = outer_joins.group_by do |join|
          case join
          when Hash, Symbol, Array
            :association_join
          when ActiveRecord::Associations::JoinDependency
            :stashed_join
          else
            raise ArgumentError, "only Hash, Symbol and Array are allowed"
          end
        end

        build_join_query(manager, buckets, Arel::Nodes::OuterJoin, aliases)
      end