Question

使用Rails 3和ActiveModel，我无法使用自我。语法来获取基于ActiveModel的对象内的属性值。

在下面的代码中，在save方法中，self.first_name求值为nil，其中@attributes [：first_name]求值为'Firstname'（初始化对象时从控制器传入的值）。

在ActiveRecord中，这似乎有效，但是当在ActiveModel中构建相同的类时，它却没有。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

我明白了。我提到的作为对Marian的答案的评论的“hack”实际上证明了如何生成ActiveRecord类的访问器。这是我做的：

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

如果你查看ActiveRecord的源代码（lib/active_record/attribute_methods/{read,write}.rb），你可以看到同样的事情。

Answer 2

您需要ActiveModel::AttributeMethods

ActiveModel字段未映射到访问者

2 个答案: