Rails 3 验证:存在 =>错误的 [英] Rails 3 Validation :presence => false

问题描述

这是我期望的一个非常简单的问题，但我无法在指南或其他地方找到明确的答案.

Here's what I expected to be a perfectly straightforward question, but I can't find a definitive answer in the Guides or elsewhere.

我在 ActiveRecord 上有两个属性.我只想要一个存在，另一个是 nil 或空白字符串.

I have two attributes on an ActiveRecord. I want exactly one to be present and the other to be nil or a blank string.

我该如何做相当于 :presence => false 的事情?我想确保该值为零.

How do I do the equivalent of :presence => false? I want to make sure the value is nil.

validates :first_attribute, :presence => true, :if => "second_attribute.blank?"
validates :second_attribute, :presence => true, :if => "first_attribute.blank?"
# The two lines below fail because 'false' is an invalid option
validates :first_attribute, :presence => false, :if => "!second_attribute.blank?"
validates :second_attribute, :presence => false, :if => "!first_attribute.blank?"

或者也许有一种更优雅的方式来做到这一点......

Or perhaps there's a more elegant way to do this...

我正在运行 Rails 3.0.9

I'm running Rails 3.0.9

推荐答案

class NoPresenceValidator < ActiveModel::EachValidator                                                                                                                                                         
  def validate_each(record, attribute, value)                                   
    record.errors[attribute] << (options[:message] || 'must be blank') unless record.send(attribute).blank?
  end                                                                           
end    

validates :first_attribute, :presence => true, :if => "second_attribute.blank?"
validates :second_attribute, :presence => true, :if => "first_attribute.blank?"

validates :first_attribute, :no_presence => true, :if => "!second_attribute.blank?"
validates :second_attribute, :no_presence => true, :if => "!first_attribute.blank?"

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