有没有一种方法来验证对一个ActiveRecord特定属性不首先实例化对象？ [英] Is there a way to validate a specific attribute on an ActiveRecord without instantiating an object first?

问题描述

例如，如果我有一个用户模式，我只需要验证登录（验证通过AJAX表单时，它可以发生），如果我使用的用户模型中定义相同的模型验证，而无需实际实例化将是巨大的用户实例。

For example, if I have a user model and I need to validate login only (which can happen when validating a form via ajax), it would be great if I use the same model validations defined in the User model without actually instantiating a User instance.

因此​​，在控制器我能写code像

So in the controller I'd be able to write code like

User.valid_attribute?(:login, "login value")

反正我能做到这一点？

Is there anyway I can do this?

推荐答案

由于验证的情况下运行（和他们使用错误的实例作为容器的错误信息属性），你不能使用它们，而无需对象实例化。说了这么多，你可以隐藏这个需要的行为放到一个类方法：

Since validations operate on instances (and they use the errors attribute of an instance as a container for error messages), you can't use them without having the object instantiated. Having said that, you can hide this needed behaviour into a class method:

class User < ActiveRecord::Base
  def self.valid_attribute?(attr, value)
    mock = self.new(attr => value)
    unless mock.valid?
      return mock.errors.has_key?(attr)
    end
    true
  end
end

现在，你可以叫

User.valid_attribute?(:login, "login value")

就像你意。

（理想情况下，你会直接包括类方法进入的ActiveRecord :: Base的，因此将提供给每一个模型。）

(Ideally, you'd include that class method directly into the ActiveRecord::Base so it would be available to every model.)

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