In order to use nested attributes in Rails 4, one must use the params.require method inside controller with the _attributes keyword and the list of fields inside the nested model. This is a good option if the keys of the nested models are known.

Here’s a simplified version of what it would look like. The question_params method inside the controller will have the nested model answer setup with answer_attributes: [:id, :response].

/controllers/question_controller.rb

class QuestionController > ApplicationController
  def new
    if params[:question].present?
      @question = Question.new(question_params)
    else
      @question = Question.new
    end
  end

private
  def question_params
    params.require(:question).permit(:id, :name, answer_attributes: [:id, :response])
  end
end

/models/question.rb

class Question > ActiveRecord::Base
has_many :answers
  accepts_nested_attributes_for :answers
end

/models/answer.rb

class Answer > ActiveRecord::Base
  belongs_to :question
end

Note: If you want to whitelist all nested parameters, you can use the code at: https://github.com/rails/rails/issues/9454#issuecomment-14167664. This would eliminate the need to list each of the nested models individually.