CODEWITHSUNDEEP
pythondjangodjango-models
Neo
Neo

Reputation: 13881

Django : Foreign key set not found after saving object

I've got a question model and mcq choices model which have foreign key to question.

class Question(models.Model):
    statement = models.TextField(max_length=1024)
    def save(self, *args, **kwargs):
        super(Question,self).save(*args,**kwargs)
        #ques = Question.objects.get(id = self.id)
        f = open('/tmp/prj/log.txt', 'w')
        choiceobjs = self.choice_set.all()
        if choiceobjs:
           f.write("choices found")
        else:
           f.write("choices not found.. zilch")
        f.close()

 class Choice(models.Model):
    value = models.TextField(max_length=1024)
    question = models.ForeignKey(Question)

Now I've overridden the save method of question. Even after the question has been saved, I cannot find choice_set in save method! I always get "choices not found.. zilch" in my logfile.

UPDATE: I'm creating my Question in Admin interface, and 'Choice' objects are being created 'inline'.

So the modified question is - In what sequence do the 'inline' fields/models and the main model get created? How can I delay my check for foreignkey set in save method, such that 'foreignkey_set' becomes visible?

Upvotes: 2

Views: 1857

Answers (1)

Reiner Gerecke
Reiner Gerecke

Reputation: 12214

class Foo(models.Model):
    pass


class Bar(models.Model):
    foo = models.ForeignKey(Foo)

When using inlines of Bar in the Foo admin, Django has to save the Foo object first, because the Bar objects need the primary key to reference it in a ForeignKey:

self.save_model(request, new_object, form, change=False)
form.save_m2m()
for formset in formsets:
    self.save_formset(request, form, formset, change=False)

http://code.djangoproject.com/browser/django/trunk/django/contrib/admin/options.py#L870

That means when Foo's save method is called, the inline Bar objects haven't been saved yet, and therefore can't be queried. So you need to work around this, if you need to access these objects when a Foo instance was saved in the admin (using Bar inlines).

One possible solution would be to attach to a post_save signal of Bar, see which Foo object it is referencing, and executing the relevant code. But this would trigger on every change, even if no Foo object was created.

Upvotes: 3

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