Ruby on rails 按和排序对象有许多关联

我有两个目标：

class Person < ActiveRecord::Base
   has_many :tests
end

class Test <ActiveRecord::Base
   belongs_to :person
end

---

一旦我有了这个问题，我该如何将其返回到玩家列表中进行排序？

这是一个老问题，但最近我试图找到类似问题的解决方案：

在rails 3中，它只是

class Person < ActiveRecord::Base
  has_many :tests
  scope :order_by_score, lambda {|direction| joins(:tests).group(:person_id).order("sum(score) #{direction}")
end
# when Person also has attribute 'score', it should be .order("sum('tests.score') #{direction}")

class-Person

老问题，但最近我试图找到类似问题的解决方案：

在rails 3中，它只是

class Person < ActiveRecord::Base
  has_many :tests
  scope :order_by_score, lambda {|direction| joins(:tests).group(:person_id).order("sum(score) #{direction}")
end
# when Person also has attribute 'score', it should be .order("sum('tests.score') #{direction}")

class-Person