ruby-on-rails – 从ActiveRecord查询返回类型

Rails允许您通过链接has_many关联来构建复杂查询.此功能的核心是一堆XXXAssocation(如HasManyAssociation)类.
当您在has_many关联上调用.class时,您的调用实际上适用于HasManyAssociation实例.但这是神奇的开始：

# collection_proxy.rb
instance_methods.each { |m| undef_method m unless m.to_s =~ /^(?:nil?|send|object_id|to_a)$|^__|^respond_to|proxy_/ }

Rails HasManyAssociation实例的undefs(隐藏)方法(除了少数,正如你在正则表达式中看到的那样)然后使用delegation和method_missing将你的调用传递给一些底层数组(如果你试图获取记录)或者关联本身(如果你链接你的协会)：

delegate :group,:order,:limit,:joins,:where,:preload,:eager_load,:includes,:from,:lock,:readonly,:having,:pluck,:to => :scoped 

  delegate :target,:load_target,:loaded?,:to => :@association

  delegate :select,:find,:first,:last,:build,:create,:create!,:concat,:replace,:delete_all,:destroy_all,:delete,:destroy,:uniq,:sum,:count,:size,:length,:empty?,:any?,:many?,:include?,:to => :@association

  def method_missing(method,*args,&block)
    match = DynamicFinderMatch.match(method)
    if match && match.instantiator?
      send(:find_or_instantiator_by_attributes,match,match.attribute_names,*args) do |r|
        proxy_association.send :set_owner_attributes,r
        proxy_association.send :add_to_target,r
        yield(r) if block_given?
      end
    end

    if target.respond_to?(method) || (!proxy_association.klass.respond_to?(method) && Class.respond_to?(method))
      if load_target
        if target.respond_to?(method)
          target.send(method,&block)
        else
          begin
            super
          rescue NoMethodError => e
            raise e,e.message.sub(/ for #<.*$/," via proxy for #{target}")
          end
        end
      end

    else
      scoped.readonly(nil).send(method,&block)
    end
  end

因此,HasManyAssociation实例决定自己要处理什么以及需要通过隐藏数组完成什么(类方法不是HasManyAssociation所感兴趣的,所以它将在这个隐藏数组上调用.结果当然是Array,有点欺骗).