如何通过对象参数为 ActiveModel Serializer 定义自定义属性？

Question

I have the following Serializer class:

class BooksSerializer < ActiveModel::Serializer
  attributes :name, :position
  attributes :pages unless object.children.present?

But it's fall down with an Error "undefined method `object' for SectionSerializer:Class". How can I get object params for these conditions?

I can get access to object only inside of function. For example:

def pages
  object.pages  ....
end

But I need to exclude some fields from Serialization by conditions.

Answer 1

I found a solution:

class BooksSerializer < ActiveModel::Serializer
  attributes :name
  def attributes(*args)
      hash = super
      hash[:pages] = pages unless object.children.present?          
      hash
  end

  def pages
   ....
  end
  ....
end

Answer 2

Here's an updated solution:

class BooksSerializer < ActiveModel::Serializer
  attributes :name
  attribute :pages, if: -> { object.children.present? }

  def pages
    ...
  end
end