按子对象排序对象数组

Question

我有一个对象数组，我需要根据子对象average_score属性对它们进行排序。我试着sort!但这似乎并没有工作，我不知道我可以在这里使用Rails的协会：

collection.sort! do |a, b| 
    a.children.where(:user_id => current_user.id).first.average_score <=> b.children.where(:user_id => current_user.id).first.average_score 
end 

任何人都可以建议我如何才能做到这一点？

Answer 1

collection.sort_by do |x| 
    x.children.where(:user_id => current_user.id).first.average_score 
end 

虽然我会寻找一个纯粹和更快的SQL解决方案。

Answer 2

当a，b是用户的情况下，我会做这个

class User 
    has_many :children 

    # This still looks smelly, has many children 
    # but only getting score of first one? 
    def children_average_score 
    first_child = self.children.where(:user_id => self.id).first 

    return first_child.nil ? 0 : first_child.average_score 
    end 
end 

然后您的排序：

collection.sort! do |a, b| 
    a.children_average_score <=> b.children_average_score 
end