正確驗證的單一性，可發佈，而不上傳

Question

我想允許沒有圖像或具有獨特的圖像發佈任何消息，我在我的模型中添加以下代碼

validates :image_fingerprint, :uniqueness => true 

它禁止張貼類似的圖像，但它禁止在沒有圖像的情況下發布多條消息。我嘗試添加

:allow_blank => true

和

:allow_nil => true

，但它會導致以下錯誤：

TypeError in PostsController#create can't convert nil into String

我怎樣才能解決呢？

Answer 1

你可以驗證使用:unless，僅當此屬性不是空白

validates :image_fingerprint, :uniqueness => true, 
    :unless => Proc.new { |a| a.image_fingerprint.blank? } 

參考：

You can associate the :if and :unless options with a symbol corresponding to the name of a method that will get called right before validation happens. This is the most commonly used option.

Finally, it’s possible to associate :if and :unless with a Proc object which will be called. Using a Proc object gives you the ability to write an inline condition instead of a separate method. This option is best suited for one-liners.

http://guides.rubyonrails.org/active_record_validations_callbacks.html#conditional-validation