什么是活动关系（等）相当于：from

Question

我的一个模型中有这个named_scope：

named_scope :latest_100,
            :from => '(select * from videos order by videos.created_at desc limit 0, 100) as videos'

它的目的是创建最后100个视频的池（返回结果为'视频'，以便其他范围对该数据集进行操作），然后我可以在此之后链接范围并从该结果池中过滤记录

# video.rb
named_scope :most_popular, :order => 'popularity'
named_scope :take_5, :limit => 5

# video_controller.rb
# it gets the latest 100 videos, then sorts those by popularity, and takes the top 5.
@videos = Video.latest_100.most_popular.take_5

是否有与Arel相同的声明？

Answer 1

Arel中存在.from（）方法。

我用以下方式使用它：

# video.rb
scope :latest_100, from('(select * from videos limit 100 order by created_at desc) as videos')
scope :most_popular, order('popularity')
scope :take_5, limit(5)

# video_controller.rb
@videos = Video.latest_100.most_popular.take_5

latest_100将创建一个有效视频池，您可以从中吸引最受欢迎的前5个。