ruby-on-rails - rails : Method for joining if a user has liked a set of songs

Question

我有以下型号:

用户

播放列表

SongLike

宋

...

当我查询播放列表的所有歌曲时，我会返回一组歌曲对象。找出用户“喜欢”哪些歌曲的最有效方法是什么？喜欢存储在 SongLike 模型中:

class SongLike < ActiveRecord::Base
  belongs_to :user
  belongs_to :song, :counter_cache => "likes_count"
end

...这是歌曲模型:

class Song < ActiveRecord::Base
  has_and_belongs_to_many :playlists
  has_many :featured_songs
  has_many :song_likes
  has_many :users, :through => :song_likes
  ...
end

Answer 1

利用您的 Song_likes 关联以及内存中的歌曲，而不是多次查询数据库:

# user.rb
def songs_liked_from(subset)
  like_ids = self.song_likes.where(:song_id => subset.map(&:id)).select(:song_id).map(&:song_id)
  subset.select{|s| liked_ids.include?(s.id) }
end