验证关联模型的特定属性

Question

验证关联模型的属性的最简单方法是什么？

Item 
    belongs_to :user 
    validates_presence_of :user 
    # AND the "is_photographer" column for that user must be true 

User 
    has_many :items 
    # can be a regular user or a photographer 

Answer 1

validate :user_is_photographer, :if => :user 

def user_is_photographer 
    errors.add(:user, "should be a photographer") unless user.is_photographer 
end