writer_method

# File activerecord/lib/active_record/aggregations.rb, line 244
        def writer_method(name, class_name, mapping, allow_nil, converter)
          define_method("#{name}=") do |part|
            klass = class_name.constantize
            unless part.is_a?(klass) || converter.nil? || part.nil?
              part = converter.respond_to?(:call) ? converter.call(part) : klass.send(converter, part)
            end

            if part.nil? && allow_nil
              mapping.each { |pair| self[pair.first] = nil }
              @aggregation_cache[name] = nil
            else
              mapping.each { |pair| self[pair.first] = part.send(pair.last) }
              @aggregation_cache[name] = part.freeze
            end
          end
        end