On Fri, Mar 09, 2007 at 10:06:52 -0500, Rick Schumeyer <rschumeyer@xxxxxxxx> wrote: > > From a business rules perspective: > Some users are not employees (like an admin user) > Some employees are not users > > I can think of two ways to do this: > > 1) a 1-1 relationship where the user table contains a FK to the employee > table. Since not all users will be employees, the FK will sometimes be > null. > In rails, the user class would "belong_to employee" while employee > "has_one user". > > 2) Create a link table that has FKs to both the user and employee > table. This make sense because I'm not sure that the concept of "there > might be a linked employee" belongs in the user table. This moves it to > a separate table designed for that purpose. But then again, it may just > be a needless extra table. > > Would you prefer one solution over the other? I think you need a linking table to properly represent the business rule above. You can use unique constraints on each key in the link table, to enforce a 1 to 1 link for the users that are employees.
