>
> For whatever reason, if a field is not provided in the request data, then
> Django is assuming it is an empty string and overwriting existing data.
>
I recently discovered that if the model field has the *default* attribute,
then the non-existent fields in the POST data will not be populated with
default values, but will remain untouched. Example:
class User(models.Model):
first_name = models.CharField(max_length=100, blank=True, default='')
last_name = models.CharField(max_length=100, blank=True)
class UserForm(forms.ModelForm):
class Meta:
model = User
fields = ('first_name', 'last_name')
user = User(first_name='John', last_name='Doe')
form = UserForm({}, instance=user)
instance = form.save()
# -> <User: first_name="John", last_name="">
I'm not sure if this is a bug or a feature, but the documentation does not
mention this point:
> If an optional field doesn’t appear in the form’s data, the resulting
> model instance uses the model field default, if there is one, for that
> field.
>
(https://docs.djangoproject.com/en/2.0/topics/forms/modelforms/#the-save-method)
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