为另一个模型的子集查找多个唯一关联模型的推荐方法是什么?例如,对于一部分用户,请确定他们所青睐的独特艺术家模型。
一种方法是从数据库中获取用户,然后迭代所有用户查询收藏夹并构建一个独特的数组,但这似乎效率低且速度慢。
class User < ActiveRecord::Base
has_many :favorites
end
class Artist < ActiveRecord::Base
has_many :favorites
end
class Favorite < ActiveRecord::Base
belongs_to :user
belongs_to :artist
end
@users = User.find_by_age(26)
# then determine unique favorited artists for this subset of users.
答案 0 :(得分:7)
has_many
关联为此要求提供了一个名为uniq
的选项:
class User < ActiveRecord::Base
has_many :favorites
has_many :artists, :through => :favorites, :uniq => true
end
class Artist < ActiveRecord::Base
has_many :favorites
has_many :users, :through => :favorites, :uniq => true
end
class Favorite < ActiveRecord::Base
belongs_to :user
belongs_to :artist
end
用法:
# if you are expecting an array of users, then use find_all instead of find_
@users = User.find_all_by_age(26, :include => :artists)
@users.each do |user|
user.artists # unique artists
end
修改1
我已根据用户的评论更新了答案。
解决方案1-:群组
Artist.all(:joins => :users, :group => :id,
:conditions => ["users.age = ?", 26])
解决方案2-选择DISTINCT
Artist.all(:joins => :users, :select => "DISTINCT artists.*",
:conditions => ["users.age = ?", 26]))