如何为控制器中的每个方法统一序列化器的输出？

我正在写一个实习项目，我们有以下序列化程序：

class PhotopostSerializer < ActiveModel::Serializer
  attributes :id, :content, :picture, :comments_count, :rating_count, :liked_by_current_user

  belongs_to :user
  has_many :comments do
    comments = []
    object.comments.each do |comment|
      comments << { id: comment.id, content: comment.content, user: { id: comment.user.id,
                                                                      first_name: comment.user.first_name,
                                                                      last_name: comment.user.last_name,
                                                                      image: comment.user.image } }
    end
    comments
  end

  def liked_by_current_user
    object.rating.pluck(:user_id).include?(instance_options[:current_user])
  end
end

在控制器中，我们有 index 和 show 方法，每个方法都需要自己的评论数（索引中只有 3 个，都在 show 中。）

试图创建几个继承自上述类的类，但给出错误 undefined method `model_name' for Photopost::ActiveRecord_Relation:Class（在控制器中指定序列化程序时）或superclass mismatch for class PhotopostShowSerializer（在删除序列化程序后第一次请求方法时）

def index
  photoposts = Photopost.custom_order(params[:order_by], params[:order_type])
  render json: photoposts, current_user: api_user.id, status: :ok
end

def show
  photopost = Photopost.find(params[:id])
  if photopost.moderating?
    if photopost.user == api_user
      render json: { message: "Post with id #{params[:id]} on moderation" }
    else
      raise ActiveRecord::RecordNotFound
    end
  else
    render json: photopost, status: :ok, current_user: @api_user.id
  end
  rescue ActiveRecord::RecordNotFound
    render json: { message: "Post with id #{params[:id]} is not found" }, status: :not_found
end

帮助，我不知道在哪里进一步挖掘