Rails4時代のnested_attributes [error]undefined method `with_indifferent_access' for…

undefined method `with_indifferent_access' for…” when passing it nested attributes

というエラーが出て、うーんRails4になって久しぶりにいじるとなにがなんだかでしたが、解決したため記録しておきます。

mongoidを使ってますが、使い方はどっちも変わらないです。笑

class Article

  include Mongoid::Document

  include Mongoid::Timestamps

  field :title, type: String

  field :sub_title, type: String

  has_many :prices

  accepts_nested_attributes_for :prices  #追加
end

class Price

  include Mongoid::Document

  field :article_id, type: String

  field :type, type: Integer

  belongs_to :article

end
class ArticleController < ActionController::Base

  def create

    @article = Article.new(article_params)　#pricesを含めて入れてくれる

    @prices = @article.prices.build(article_params["prices"]) #不要

    @prices.save　#不要

    respond_to do |format|

      if @article.save

        format.html { redirect_to @article, notice: 'Article was successfully created.' }

        format.json { render action: 'show', status: :created, location: @article }

      else

        format.html { render action: 'new' }

        format.json { render json: @article.errors, status: :unprocessable_entity }

      end

    end
end

  private


  def article_params

    params.require(:article).permit(:title, :sub_title, prices_attributes: [:type]) #attribute名に注意

  end
end

<参考>
 Rails 4 permit nested attributes doesn't create/update || stackoverflow

“NoMethodError (undefined method `with_indifferent_access' for…” when passing it nested attributes || stackoverflow

Rails 4 Nested Attributes Unpermitted Parameters || stackoverflow

Strong Parameters || Rails公式サイト