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Tracking stale fields on a Django model instance

Project description

Django Stale Fields

Tracking changed fields on a Django model instance.

Makes a Mixin available that will give you the properties:

- `is_stale`
- `stale_fields`

As well as the methods:

- `save_stale()`

Which will will selectively only update stale columns using the familiar
`Model.objects.filter(pk=pk).update(**stale_fields)` pattern (but still
resolves `F()` or `auto_now` constructs).


Install the package using [pip][]. Then use the instructions in "Using
the Mixin in the Model".

$ pip install django-stalefields

or if you're interested in developing it, use [virtualenv][] and
[virtualenvwrapper][]. The default `` will look for the
stalefields package in its current location.

$ mkvirtualenv django-stalefields
(django-stalefields)$ pip install -r example_app/requirements.pip
(django-stalefields)$ example_app/ test testing_app

Using the 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)$ ./ shell
>>> from testing_app.models import TestModel
>>> tm = TestModel(boolean=True, characters="testing")
>>> tm.is_stale
>>> tm.stale_fields
>>> tm.boolean = False
>>> tm.is_stale
>>> tm.stale_fields
('boolean', )
>>> tm.characters = "have changed"
>>> tm.is_stale
>>> tm.stale_fields
('boolean', 'characters', )
>>> tm.save_dirty()
>>> tm.is_stale
>>> tm.get_stale_fields

Why would you want this?

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.


This code has largely be adapted from what was made available at [Stack Overflow][].

[Stack Overflow]:

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