how to set foreign key during form completion (python/django)

During form processing I’d like to be able to set a foreign key field on a model object without the user having to select the key from a dropdown.

For instance:

#models.py
class AAA(models.Model):

    some_field = models.TextField()

class BBB(models.Model):
    another_field = models.TextField()
    key_field = models.ForeignKey('AAA')

The user will navigate from a view showing an instance of ‘AAA’ to a create_object style view that will create an instance of ‘BBB’ given a parameter referring to ‘AAA’. The foreign key is set in code to point back to the ‘AAA’ instance.

The django comments framework seems to do this but I can’t figure out how.

Any ideas? I’m sure it should be quite simple.

Answer

You can exclude the key_field from your model form, save with commit=False, then set key_field in your view before saving to the database.

class BBBForm(forms.ModelForm):
    class Meta:
        model = BBB
        exclude = ("key_field",)

def create_view(request, **kwargs):
    if request.method == "POST":
        aaa = # get aaa from url, session or somewhere else
        form = BBBForm(request.POST)
        if form.is_valid():
            bbb = form.save(commit=False)
            bbb.key_field = aaa
            bbb.save()
            return HttpResponseRedirect("/success-url/")
        ...