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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).


Installing
==========

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 `settings.py` 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/manage.py test testing_app
```



Using the Mixin in the Model
============================

```python
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
=====================

```bash
(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()
>>> tm.is_stale
False
>>> 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.

Credits
=======

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


[pip]: http://www.pip-installer.org/en/latest/
[virtualenv]: https://pypi.python.org/pypi/virtualenv
[virtualenvwrapper]: https://pypi.python.org/pypi/virtualenvwrapper
[signals]: http://docs.djangoproject.com/en/1.2/topics/signals/
[pressave]: http://docs.djangoproject.com/en/1.2/ref/signals/#django.db.models.signals.pre_save
[Stack Overflow]: http://stackoverflow.com/questions/110803/stale-fields-in-django

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