build

# File activerecord/lib/active_record/associations/join_dependency.rb, line 128
      def build(associations, parent = nil, join_type = Arel::InnerJoin)
        parent ||= join_parts.last
        case associations
        when Symbol, String
          reflection = parent.reflections[associations.intern] or
          raise ConfigurationError, "Association named '#{ associations }' was not found on #{ parent.base_klass.name }; perhaps you misspelled it?"
          unless join_association = find_join_association(reflection, parent)
            @reflections << reflection
            join_association = build_join_association(reflection, parent)
            join_association.join_type = join_type
            @join_parts << join_association
            cache_joined_association(join_association)
          end
          join_association
        when Array
          associations.each do |association|
            build(association, parent, join_type)
          end
        when Hash
          associations.keys.sort_by { |a| a.to_s }.each do |name|
            join_association = build(name, parent, join_type)
            build(associations[name], join_association, join_type)
          end
        else
          raise ConfigurationError, associations.inspect
        end
      end