Enforcing unique foreign key in Django subclass but not in base class

manpreet Best Answer 2 years ago

I'm writing a website to host online educational material for a university. I'm using the following data model:

class Department(models.Model):
    #snip - remaining fields involve department names, acronyms, etc.

class Course(models.Model):
    department = models.ForeignKey(Department)
    #snip

class Resource(models.Model):
    # generic class for course syllabuses, exams, homework, and other documents
    course = models.ForeignKey(Course)

class Syllabus(Resource):
    #snip - fields for titles, URLs, and the like

class Homework(Resource):
    #snip - similar fields to above

# and other similar subclasses

Every resource subclass (syllabus, homework, etc.) is associated with one course through the Course foreign key in the base Resource class. I want to enforce uniqueness of the foreign key for the Syllabus subclass (i.e. allow only one syllabus per course), but not for the other subclasses, and keep the class hierarchy intact.

I tried searching around for solutions, but I couldn't find anything that seemed promising, although it could be my lack of Django experience getting in the way. I'd appreciate any quick help.