CODEWITHSUNDEEP
pythondjangodjango-orm
Vladimir Solovyov
Vladimir Solovyov

Reputation: 307

Does django know what fields were updated?

I'm trying to find out how django's save() works. And there is some thing I can't understand. Is there any way to know what field is updating at the moment?

The best way I know is use pre_save() signal and do smth like this:

current_field_val = instance.my_field
old_field_val == sender.objects.get(pk=instance.pk).my_field
if current_field_val != old_field_val:
    # do smth

But I don't want to select from DB. And how DjangoORM knows what field needs to be updated, or it updates all fields in the model(it seems to me it's strange behaviour).

Upvotes: 1

Views: 235

Answers (2)

SaeX
SaeX

Reputation: 18691

In a view, you can use form.changed_data to find out which data is changed in the form.

E.g.

if 'yourfield' in form.changed_data`:
    (do something)

Upvotes: 1

Hasan Ramezani
Hasan Ramezani

Reputation: 5194

you can use something like this:

class myClass(models.Model):
    my_field = models.CharField()

    __my_field_orig = None

    def __init__(self, *args, **kwargs):
        super(myClass, self).__init__(*args, **kwargs)
        self.__my_field_orig = self.my_field

    def save(self, force_insert=False, force_update=False, *args, **kwargs):
        if self.my_field != self.__my_field_orig:
            # my_field changed - do something here

        super(myClass, self).save(force_insert, force_update, *args, **kwargs)
        self.__original_name = self.name

Upvotes: 0

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