For example I have a relationship like this: user (0..*) buys product (0..*)
Which results in an association class, called sale, which has the userID and productID. Just for the question's sake, imagine this sale class has NO other attributes, except for these IDs.
My question is, should I show this sale class in my class diagram? Or can I just leave it and only show the relationship.
Although I have never seen this done before, I am asking because someone told me you don't need to show the association class if it has no relationship attributes.