photo_serializer.rb

class PhotoSerializer < ActiveModel::Serializer
  attributes :id, :created_at, :photo_url_thumb, :photo_url_large

  # Only include these if it is coming from the show action
  has_many :likes
  has_many :tags
  has_many :comments

end

photos_controller.rb

class PhotosController < ApplicationController
  def index
    render json: Photo.all
  end

 def show
   render json: Photo.where(id: params[:id]).includes(:comments, :tags, :likes).first
 end
end