ModelForm primary_key update with instance set is executed as INSERT caused by is_valid() chaning the instance

[amin@…]

I do agree this is a bad database design but it's executed without any warning or anything in the docs so i want to open this ticket to allow the discussion of raising an Error or anything (e.g. an info in the docs @primary_key or modelform) not let anyone run into this mistake.

class Test(models.Model):

email = models.CharField(max_length=100, primary_key=True)

class TestForm(forms.ModelForm):

class Meta:

model = Test

# assuming this object exists
x = Test.objects.get(email='old@…')

form = TestForm(email='new@…', instance=x)

# here instance is updated with new@… as pkey and django thinks it has to create a new model instance not updating the old instance
if form.is_valid():

new_x = form.save()
new_x.save()