title: Ruby on rails invitation / enrollment
body: <p>I am currently building an application where part of it is an invitation / enrollment system. Currently there are "courses" and "classrooms" in the system. A "course" is thus some course, and a "classroom" is a specific instance of a course. F.ex. there might be 1 course, but 3 classroom instances of that course, having different start/end dates, slightly different/updated materials, etc. Now, an "employee" can be invited to participate in a "course", but the "employees" themselves, has to choose a specific "classroom" to enroll in. So, the employee goes to his/hers profile page, where the invitations show up. Now the employee clicks an invitation, and can then choose a specific classroom to enroll in. This should obviously create an enrollment. But, it should also get rid of the invitation, since it has been "accepted". Currently i have it set so that "employees" has many "classrooms" through "enrollments". Also, an "employee" has many "courses" through "invitations". This doesn't seem right though, since when an employee clicks some invitation, they will be taken to an enrollment page(enrollment controller), where an enrollment will be created. As the enrollment is created, the invitation should be deleted though. So right now i guess the enrollment controller should be able to create enrollments and delete invitations. This seems like bad design. I am pretty happy with the relation between classrooms and employees, but the relation between employees and invitations seems bad. How would you do it? </p>