按子對象排序對象數組

Question

我有一個對象數組，我需要根據子對象average_score屬性對它們進行排序。我試着sort!但這似乎並沒有工作，我不知道我可以在這裏使用Rails的協會：

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 

任何人都可以建議我如何才能做到這一點？

Answer 1

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

雖然我會尋找一個純粹和更快的SQL解決方案。

Answer 2

當a，b是用戶的情況下，我會做這個

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 

然後您的排序：

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