NOT NULL constraint failed: users_details.user_id - django

Question

I've tried to add another details form that have address and birth date on my registration form page. Every time i tried to sign up i get the NOT NULL constraint failed error.
models.py
class Details(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
address = models.CharField(max_length=60, blank=True)
birth_date = models.DateField(null=True, blank=True)
views.py
def register(request):
if request.method == 'POST':
r_form = UserRegisterForm(request.POST)
o_form = DetailsForm(request.POST)
if r_form.is_valid and o_form.is_valid():
r_form.save()
o_form.save()
username = r_form.cleaned_data.get('username')
messages.success(request, f'Your account has been created!')
return redirect('login')
else:
r_form = UserRegisterForm()
o_form = DetailsForm()
context = {
'r_form' : r_form,
'o_form' : o_form
}
return render(request, 'users/register.html', context)
forms.py
class UserRegisterForm(UserCreationForm):
email = forms.EmailField()
class Meta:
model = User
fields = ['username', 'email','password1', 'password2']
class DetailsForm(forms.ModelForm):
address = forms.CharField()
birth_date = forms.DateField()
class Meta:
model = Details
fields = ['address', 'birth_date']
ERROR

Answer 1

While extraneous details/profile "sidecar" models are not the best practice since pluggable user models came along, this particular problem is caused by the two models not being associated.
Try
if r_form.is_valid and o_form.is_valid():
user = r_form.save()
o_form.instance.user = user
o_form.save()