我怎样才能确保我的has_many的大小至少为2？

Question

A has_many B

validates :b, ? # 

我究竟能检查到我至少有2个B？

Answer 1

Rails 3？尝试：

validates :b, :length => { :minimum => 2 }

Answer 2

从this answer你可以做到：

validate :has_at_least_two_potatoes?

def has_at_least_two_potatoes?
  errors.add_to_base "Model must have at least 2 potatoes" if self.potatoes.size < 2
end