sql - 如何按关联计数过滤？

Question

假设我有这样的模型:

class Foo < ActiveRecord::Base
    has_many :bars, :through => :cakes
    has_many :cakes
end

class Bar < ActiveRecord::Base
    has_many :foos, :through => :cakes
    has_many :cakes
end

class Cake < ActiveRecord::Base
    belongs_to :foo
    belongs_to :bar
end

我如何获得所有有 10 个或更多巧克力棒(因此有 10 个或更多蛋糕)的 foos？

Answer 1

Foo.all(:joins => :cakes, 
  :group => "cakes.foo_id", 
  :having => "count(cakes.bar_id) >= 10")