how to use model?

[eluser]crumpet[/eluser]
frank maybe you can answer a question for me too..
I am writing a function to display a view of a product right now. In the controller i have code to determine what privileges the user has to that product so it can decide what to display. Should this be in the model? My instinct was to put it there however then it makes my database calls less efficient, becuase I have already fetched the information about the product and stored it in a variable $product. I can do tests like $this->session->userdata('USER_ID') == $product['author']. If i make a model function called getUserAccess() or something then it will have to make an extra query to get information I have already queried... hope this makes sense