Tracking dirty fields on a Django model instance.

Dirty means that there is a difference between field value in the database and the one we currently have on a model instance.

$ pip install django-dirtyfields

To use django-dirtyfields, you need to:

• Inherit from DirtyFieldMixin in the Django model you want to track.

from django.db import models
from dirtyfields import DirtyFieldsMixin

class TestModel(DirtyFieldsMixin, models.Model):
    """A simple test model to test dirty fields mixin with"""
    boolean = models.BooleanField(default=True)
    characters = models.CharField(blank=True, max_length=80)

- Use one of these 2 functions to know if the instance is dirty, and get the dirty fields:

• is_dirty()
• get_dirty_fields()

$ ./manage.py shell
>>> from tests.models import TestModel
>>> tm = TestModel.create(boolean=True,characters="testing")
>>> tm.is_dirty()
False
>>> tm.get_dirty_fields()
{}

>>> tm.boolean = False
>>> tm.is_dirty()
True
>>> tm.get_dirty_fields()
{'boolean': True}

By default, dirty functions are not checking foreign keys. If you want to also take these relationships into account, use check_relationship parameter:

$ ./manage.py shell
>>> from tests.models import TestModel
>>> tm = TestModel.create(fkey=obj1)
>>> tm.is_dirty()
False
>>> tm.get_dirty_fields()
{}
>>> tm.fkey = obj2

>>> tm.is_dirty()
False
>>> tm.is_dirty(check_relationship=True)
True

>>> tm.get_dirty_fields()
{}
>>> tm.get_dirty_fields(check_relationship=True)
{'fkey': 1}

When using signals, especially pre_save, 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.

If you're interested in developing it, you can launch project tests on that way:

$ pip install tox
$ pip install -e .
$ tox

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