This project is no longer maintained, but we recommend looking at django-dirtyfields
Django Stale Fields
Tracking changed fields on a Django model instance.
Makes a Mixin available that will give you the properties:
As well as the methods:
Which will will selectively only update stale columns using the familiar
Model.objects.filter(pk=pk).update(**stale_fields) pattern (but still
Install the package using pip. Then use the instructions in "Using the Mixin in the Model".
$ pip install django-stalefields
$ mkvirtualenv django-stalefields (django-stalefields)$ pip install -r example_app/requirements.pip (django-stalefields)$ example_app/manage.py test testing_app
Auto-Mixin For All Models
You need to set make two
# settings.py INSTALLED_APPS = ( 'stalefields', # must be first! # the rest... ) AUTO_STALE_FIELDS = True
This provides the methods and functionality automatically for all registered models.
Manual Mixin in the Model
from django.db import models from stalefields import StaleFieldsMixin class TestModel(StaleFieldsMixin, models.Model): """A simple test model to test stale fields mixin with""" boolean = models.BooleanField(default=True) characters = models.CharField(blank=True, max_length=80)
Using it in the shell
(django-stalefields)$ ./manage.py shell >>> from testing_app.models import TestModel >>> tm = TestModel(boolean=True, characters="testing") >>> tm.save() >>> tm.is_stale False >>> tm.stale_fields () >>> tm.boolean = False >>> tm.is_stale True >>> tm.stale_fields ('boolean', ) >>> tm.characters = "have changed" >>> tm.is_stale True >>> tm.stale_fields ('boolean', 'characters', ) >>> tm.save_dirty() # just saves the dirty fields via .update() >>> tm.is_stale False >>> tm.get_stale_fields ()
Why would you want this?
- Bug avoidance
When using signals, especially pressave, it is useful to be able to see what fields have changed or not. A signal could change its behaviour depending on whether a specific field has changed, whereas otherwise, you only could work on the event that the model's save() method had been called.
Any time you call boring old
save() inside Django, all columns are inserted
once again, which can be very heavy if, for example, you have lots of text in one
column or many indexes that don't need to be needlessly checked for updating. Only
updating changing columns via
update() is much faster, but requires lots of state
monitoring of your own accord. Put simply, this is nicer you your database!
Finally, if multiple threads call
save() for different operations, only the more
recent thread wins. If they both INSERTED only their column's changing values, that wouldn't
be an issue! These kinds of bugs are a nightmare to chase down...
This code has largely be adapted from what was made available at Stack Overflow and adapted from Forked from https://github.com/smn/django-dirtyfields and https://github.com/callowayproject/django-dirtyfields..