Ruby on Rails to_json function add parameter to methods for render in favorites or not?

How do I add parameters to methods for rendering the current place in favorites?

I tried this:

class Place < ActiveRecord::Base 
   has_and_belongs_to_many :users

   def in_fav(user)
      if user.places.include?Place.find(id)
         return true
      else
         return false
      end
   end

end


class User < ActiveRecord::Base 
   has_and_belongs_to_many :places
end



class PlacesController < ApplicationController
     places = Place.all

     user = User.first

     render json: {desc:true, status:1; data: places}.to_json(:methods => :in_fav(user))
end

I find same problem here

attr_accessor :current_user

def is_favorited_by_user?(user=nil)
   user ||= current_user
end


@drops.current_user = current_user
render :json => @drops.to_json(:methods => :is_favorited_by_user?)

I don't understand current_user - it's assocciations? and how to use method current_user for collection @drops