Re: Package that helps update only changed fields

Hello Dan,

I'm not aware of any third party library handling this but a simple way to achieve

what you're after would be to subclass ModelForm in order to override save()

and pass commit=False in your super() call.

e.g. (untested)

class UpdateFieldsModelForm(ModelForm):

    update_fields = None

    def save(self, commit=True):

        instance = super().save(commit=False)

        if commit:

            update_fields = None if instance._state.adding else self.update_fields

            instance.save(update_fields=self.update_fields)

        return instance

Cheers,

Simon

Le mardi 18 juin 2019 11:38:53 UTC-4, Dan Davis a écrit :

So, I recently observed that a Django ModelForm updates all columns when it is updating a model instance. This is appropriate for a typical situation where Django is also in control of the schema.

I also see that you can control this behavior by passing update_fields to the save method, in a particular form:

    self.instance.save(update_fields=self.changed_data)

I have some complicated forms that have non-model fields and many-to-many fields mixed in there.   I'm wondering whether there is a module for Django out there that gives me some base ModelForms that do not update all fields, but only changed fields.  I am asking because I don't want to work hard to handle corner cases if there's something already out there.   What I already have is hard-coded to the form where I've made this change to do only a limited update.

Thanks,

-Dan

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