How to tell if a fields was modified

[Matias]

Hi,

How can I tell which model fields have been modified (this is, the
difference between the Model instance and the data originally retrieved
from the database) from inside the model's save() method?

Any idea?

Thanks a lot!

[Randy Barlow]

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Matias declared:

> How can I tell which model fields have been modified (this is, the
> difference between the Model instance and the data originally retrieved
> from the database) from inside the model's save() method?

You can always retrieve the model by it's primary key from the db, and
then compare self to it. Something like:

def save(stuff_and_junk):
existing_instance = self.__class__.objects.get(id=self.id)
if existing_instance.attribute != self.attribute:
print 'Holy Crap!'
super(self.__class__, self).save(stuff_and_junk)

- --
Randy Barlow
Software Developer
The American Research Institute
http://americanri.com
919.228.4971
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[Tim Chase]

>> How can I tell which model fields have been modified (this is, the
>> difference between the Model instance and the data originally retrieved
>> from the database) from inside the model's save() method?
>
> You can always retrieve the model by it's primary key from the db, and
> then compare self to it. Something like:
>
> def save(stuff_and_junk):
> existing_instance = self.__class__.objects.get(id=self.id)
> if existing_instance.attribute != self.attribute:
> print 'Holy Crap!'
> super(self.__class__, self).save(stuff_and_junk)

Remembering, of course, that get() can throw an exception if
you're creating a new object...

-tim

[ankit rai]

use clean method and use self.instance.fieldname to know previous value and then compare with the new value.