CODEWITHSUNDEEP
pythondjangoinheritance
Fuad
Fuad

Reputation: 1509

Django, Initialize a field in child class from value in parent class

In Django,

Say I have two classes, A and B.

B is the child of A. I want there to be an integer field in B that is the pk of A. I want this field in B to be initialized as such whenever I create a B object.

Thanks.

p.s. essentially I want to be able to access the pk of the parent object from the child class. If there is an easier/better way, please advise

Upvotes: 0

Views: 767

Answers (2)

Brandon Taylor
Brandon Taylor

Reputation: 34553

If you're leveraging a ModelForm to create the instance of B, you can pass in the instance of A to your form and set the value there. This way you don't have to set it in the view code.

You'll also want to exclude the a field from the B_Form

class B_Form(forms.ModelForm):
    class Meta():
        exclude = ('a',)

    def __init__(self, *args, **kwargs):
        self.a = kwargs.pop('a')
        super(B_Form, self).__init__(*args, **kwargs)

    def save(self, force_insert=False, force_update=False, commit=True):
        instance = super(B_Form, self).save(commit=False)
        instance.a = self.a

        if commit:
            instance.save()
        return instance

and to leverage this form class in a view:

from your_app.forms import B_Form

def your_view(request, a_pk):
    a = get_object_or_404(A, pk=a_pk)
    b_form = B_Form(request.POST or None, a=a)

    if request.method == 'POST' and b_form.is_valid():
        b_form.save()

    return render('your-template.html', {'b_form': b_form})

Upvotes: 0

Martin Lear
Martin Lear

Reputation: 272

you need to set up class A as a foreign key to class B

class B(models.Model):
    a = models.ForeignKey(A)
    ...

new b = B.objects.create(a=instance_of_class_a, ...)

Upvotes: 3

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