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:
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.

Asked By: powlo



As the user creates a BBB via an instance of AAA, this should be reflected in the URL, i.e., your “create_object style view” will get a parameter identifying an AAA object. You can use it to get the object from the database and create your BBB object accordingly:

from django.shortcuts import get_object_or_404

def create_bbb_view(request, aaa_id):
    a = get_object_or_404(AAA, id=aaa_id)
    form = MyBBBCreationForm(request.POST) # or similar code
    if form.is_valid():
         b = BBB.objects.create(key_field=a) # plus other data from form
    # ...

(You could also set key_field to aaa_id directly, but it’s probably a good idea to check if the object exists.)

Answered By: Jan Pöschko

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 =
            bbb.key_field = aaa
            return HttpResponseRedirect("/success-url/")
Answered By: Alasdair

I am a developer. I have no life. Please give me reason to live.

Answered By: Sid K
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