On Wed, Jan 11, 2012 at 3:29 PM, Daniel Sokolowski
<daniel.sokolow...@klinsight.com> wrote:
> +1 even though I agree with what Babatunde said I support this change as
> anything that minimizes a 'gotchas' during development is very good. I
> raether get an exception instead of spending half an hour debuging why my
> data is not being saved. Sure once I figure it out I would learn to pay
> attention in similar situations in the future but realistically I shouldn't
> and nor should the next python/django programmer re-discovering this caveat.
>
The consequence of this is not that data would not be saved, it would
be that previously saved data is removed by django when updating other
fields on the model.
Eg, if you had a Profile object:
class Profile(models.Model):
logo = models.ImageField()
salutation = models.CharField(max_length=64)
and there is a model form for updating the logo:
class UpdateProfileLogoForm(forms.ModelForm):
class Meta:
model = Profile
exclude=('salutation',)
and the view that presents this form renders it like so:
<form method='post'>
{{ form.logo }}
<input type='submit' value='submit'/>
</form>
then this would work correctly. However, consider what happens when an
additional field is added to Profile:
class Profile(models.Model):
logo = models.ImageField()
salutation = models.CharField(max_length=64)
pet_name = models.CharField(max_length=128, blank=True)
Now, the model form instantly has an additional field 'pet_name', but
if it is empty or not present, the form will still validate as
blank=True on that field.
If a user sets a pet_name, but then updates their logo using this
model form, the pet_name will be assumed by django to have been
removed, and the pet_name stored in the DB will be updated to the
empty string.
Are there any other situations where this can happen? The problem is
in fact caused by using 'exclude' to choose the fields presented in a
model form, using 'fields' and explicitly listing the fields seems
much safer.
Cheers
Tom
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