如何通过关联计数过滤？

Question

假设我的模型看起来像这样:

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

我怎样才能得到10个或更多棒(因此有10个或更多个蛋糕)的所有foos？

Answer 1

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