我如何確保我的has_many的尺寸至少爲2？

Question

A has_many B 

validates :b, ? # 

我究竟能夠檢查至少有2個B？

Answer 1

從this answer你應該能夠做到：

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 

Answer 2

Rails 3的？試試：

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