[Django]-Why does form.is_valid() update the related model for Django ModelForms?

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I believe the reason is this:

The first time you call is_valid() or
access the errors attribute of a
ModelForm has always triggered form
validation, but as of Django 1.2, it
will also trigger model validation.
This has the side-effect of cleaning
the model you pass to the ModelForm
constructor. For instance, calling
is_valid() on your form will convert
any date fields on your model to
actual date objects.

From here. Logically, this does actually make sense. Suppose I have a model like this:

class SomeModel(models.Model):
    Somefield = models.CharField(unique=True)

Then as far as the modelform is concerned, validating the field TextInputField would work for any value. However, from the model’s perspective, not any value will do – that value must be unique.

The validation mechanisms are described here. Basically, calling full_clean on a model causes that model to check its own fields as per the OO paradigm. So for this reason, the in memory image of the model can be updated and validating it will check it can actually be written to the database.

Thus it makes sense, because your guard:

if form.is_valid():

Really ought to ensure that:

    form.save()

Can actually happen.

👤user257111

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