Re: Modify only one field

On Feb 4, 9:10 am, Ashe <matthieu....@gmail.com> wrote:
> Is there a better solution to modify only the specified field on a
> table than :
> self.__class__.objects.filter(id=self.id).update(myfield='new awesome
> value')
> ?
> I have been looking for a cleaner solution for a long time without
> success, while waiting for that (https://code.djangoproject.com/ticket/4102
> ).
>
> If it is the best solution, is there any drawback with that solution ?
> I suppose there is a read on the database because of the
> objects.filter(). And we lose the possibility to use save() and
> clean() before update, which I usually enjoy to override.

That is the only available solution currently, apart of raw SQL which
is an often overlooked alternative.

You could do that update in an overridden .save method. Make it take a
kwarg 'update_fields=[],' or 'only_myfield=False'. Then, you can just
use model.save(only_myfield=True). The save method could then handle
all the necessary dirty details.

BTW even if there is a filter operation, there will be just only one
query. Actually, your method will be more effective than normal save,
as without force_update the current implementation of .save() needs to
first do a select, then update. You can see the queries made by using
django-debug-toolbar, or just by running this in the shell:
from django.db import connection
from django.conf import settings
settings.DEBUG = True
self.__class__.objects.filter(id=self.id).update(myfield='new awesome
value')
print connection.queries

- Anssi

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