join_constraints

# File activerecord/lib/active_record/associations/join_dependency.rb, line 107
      def join_constraints(outer_joins)
        joins = join_root.children.flat_map { |child|
          make_inner_joins join_root, child
        }

        joins.concat outer_joins.flat_map { |oj|
          if join_root.match? oj.join_root
            walk join_root, oj.join_root
          else
            oj.join_root.children.flat_map { |child|
              make_outer_joins oj.join_root, child
            }
          end
        }
      end