为另一个模型的子集找到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,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,然后迭代它们所有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.
解决方法
has_many关联有一个名为uniq的选项用于此要求：
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,: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
编辑1
解决方案1-：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.*",26]))