Setting default value for Foreign Key attribute

django foreign-keys default
Primal Pappachan picture Primal Pappachan · Feb 16, 2012 · Viewed 73.7k times · Source

What is the best way to set a default value for a foreign key field in a model? Suppose I have two models, Student and Exam with student having exam_taken as foreign key. How would I ideally set a default value for it? Here's a log of my effort

class Student(models.Model):
   ....
   .....
   exam_taken = models.ForeignKey("Exam", default=1)

Works, but have a hunch there's a better way.

def get_exam():
    return Exam.objects.get(id=1)

class Student(models.Model):
    ....
    .....
    exam_taken = models.ForeignKey("Exam", default=get_exam)

But this fails with tables does not exist error while syncing.

Any help would be appreciated.

Answer

Gareth picture Gareth · Feb 16, 2012

In both of your examples, you're hard-coding the id of the default instance. If that's inevitable, I'd just set a constant.

DEFAULT_EXAM_ID = 1
class Student(models.Model):
    ...
    exam_taken = models.ForeignKey("Exam", default=DEFAULT_EXAM_ID)

Less code, and naming the constant makes it more readable.

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