update .exists syntax when using mongoid

venshop_app/app/controllers/sessions_controller.rb

@@ -4,7 +4,7 @@ class SessionsController < ApplicationController
   end
 
   def create
-    user = User.find_by(email: params[:session][:email].downcase)
+    user = User.find_by(email: params[:session][:email].downcase) if User.where(email: params[:session][:email].downcase).exists?
     if user && user.authenticate(params[:session][:password])
       sign_in user
       redirect_back_or user

venshop_app/app/controllers/users_controller.rb

@@ -13,7 +13,7 @@ class UsersController < ApplicationController
   end
 
   def show
-    if User.exists?(params[:id])
+    if User.where(id: params[:id]).exists?
       @user = User.find(params[:id])
     else
       flash[:error] = "Invalid user!"