how to use includes? with belongs_to relationship, ERROR = undefined method `includes?' for

my user model is as shown below user.rb

has_many :authorised_downloads, 
:class_name=>"Downloads",
:primary_key => 'id', 
:foreign_key=> :authorised_user_id

downloads model download.rb

belongs_to :authorised_users, 
:class_name => "User",
:primary_key => 'id',
:foreign_key=> :authorised_user_id

downloads controller

def download
@download = Download.find(params[:id])
if @download.authorised_users.includes?(current_user)
  send_file(@download.upload_file.path,
  :filename => @download.name,       
  :x_sendfile=>true,
  :url_based_filename => true )               
  flash[:notice] = "Your file has been downloaded"
else
   flash[:notice] = "You must buy the product first!"
end
end

in my downloads view, when i click the download link, the line if @download.authorised_users.includes?(current_user) in the download controller is highlighted with the following error

undefined method `includes?' for #<User:0x00000005c2ff10>

I dont understand where i when wrong. Your assistance will be highly appreciated

Solution

@download.authorised_users return an instance of User, not collection. B/c belongs_to :authorised_users

Try:

belongs_to :authorised_user, :class_name => "User"

And in controller:

if @download.authorised_user == current_user