ruby - ActiveModel 字段未映射到访问器

Question

使用 Rails 3 和 ActiveModel，我无法使用 self.用于获取基于 ActiveModel 的对象中属性值的语法。

在下面的代码中，在 save 方法中，self.first_name 的计算结果为 nil，其中 @attributes[:first_name] 的计算结果为 'Firstname'(初始化对象时从 Controller 传入的值)。

在 ActiveRecord 中，这似乎可行，但在 ActiveModel 中构建相同的类时，却行不通。如何在基于 ActiveModel 的类中使用访问器引用字段？

class Card
  include ActiveModel::Validations
  extend ActiveModel::Naming 
  include ActiveModel::Conversion
  include ActiveModel::Serialization
  include ActiveModel::Serializers::Xml

  validates_presence_of :first_name

  def initialize(attributes = {})
    @attributes = attributes
  end

  #DWT TODO we need to make sure that the attributes initialize the accessors properyl, and in the same way they would if this was ActiveRecord
  attr_accessor :attributes, :first_name

  def read_attribute_for_validation(key)
    @attributes[key]
  end

  #save to the web service
  def save
    Rails.logger.info "self vs attribute:\n\t#{self.first_name}\t#{@attributes["first_name"]}"
  end

  ...

end

Answer 1

我想通了。我在对 Marian 的回答的评论中提到的“hack”实际上是如何生成 ActiveRecord 类的访问器的。这是我所做的:

class MyModel
  include ActiveModel::AttributeMethods

  attribute_method_suffix  "="  # attr_writers
  attribute_method_suffix  ""   # attr_readers

  define_attribute_methods [:foo, :bar]

  # ActiveModel expects attributes to be stored in @attributes as a hash
  attr_reader :attributes

  private

  # simulate attribute writers from method_missing
  def attribute=(attr, value)
    @attributes[attr] = value
  end

  # simulate attribute readers from method_missing
  def attribute(attr)
    @attributes[attr]
  end
end

如果查看 ActiveRecord 的源代码 (lib/active_record/attribute_methods/{read,write}.rb)，您会看到同样的事情。