fix error occured when using mongodb

venshop_app/app/controllers/cards_controller.rb

@@ -7,7 +7,7 @@ class CardsController < ApplicationController
       @card_infos = session[:SHOPPING_CARD_SESSION_NAME]
     end
     unless params[:product_id].blank?
-      if Product.exists?(params[:product_id])
+      if Product.where(id: params[:product_id]).exists?
         # if remove a product from card
         if !params[:card_action].blank? && params[:card_action] == 'remove'
           # Nothing to delete
@@ -183,7 +183,7 @@ class CardsController < ApplicationController
   end
 
   def thankyou
-    if params[:card_id].blank? || !MyCard.exists?(params[:card_id])
+    if params[:card_id].blank? || !MyCard.where(id: params[:card_id]).exists?
       flash[:error] = "Invalid card request"
       redirect_to root_path and return
     end