django-field-history

A Django app to track changes to a model field. For Python 2.7/3.4+ and Django 1.11/2.0+.

Other similar apps are django-reversion and django-simple-history, which track all model fields.

Documentation

The full documentation is at https://django-field-history.readthedocs.io.

Features

• Keeps a history of all changes to a particular model's field.
• Stores the field's name, value, date and time of change, and the user that changed it.
• Works with all model field types (except ManyToManyField).

Quickstart

Install django-field-history:

pip install django-field-history

Be sure to put it in INSTALLED_APPS.

INSTALLED_APPS = [
    # other apps...
    'field_history',
]

Then add it to your models.

from field_history.tracker import FieldHistoryTracker

class PizzaOrder(models.Model):
    STATUS_CHOICES = (
        ('ORDERED', 'Ordered'),
        ('COOKING', 'Cooking'),
        ('COMPLETE', 'Complete'),
    )
    status = models.CharField(max_length=64, choices=STATUS_CHOICES)

    field_history = FieldHistoryTracker(['status'])

Now each time you change the order's status field information about that change will be stored in the database.

from field_history.models import FieldHistory

# No FieldHistory objects yet
assert FieldHistory.objects.count() == 0

# Creating an object will make one
pizza_order = PizzaOrder.objects.create(status='ORDERED')
assert FieldHistory.objects.count() == 1

# This object has some fields on it
history = FieldHistory.objects.get()
assert history.object == pizza_order
assert history.field_name == 'status'
assert history.field_value == 'ORDERED'
assert history.date_created is not None

# You can query FieldHistory using the get_{field_name}_history()
# method added to your model
histories = pizza_order.get_status_history()
assert list(FieldHistory.objects.all()) == list(histories)

# Or using the custom FieldHistory manager
histories2 = FieldHistory.objects.get_for_model_and_field(pizza_order, 'status')
assert list(histories) == list(histories2)

# Updating that particular field creates a new FieldHistory
pizza_order.status = 'COOKING'
pizza_order.save()
assert FieldHistory.objects.count() == 2

updated_history = histories.latest()
assert updated_history.object == pizza_order
assert updated_history.field_name == 'status'
assert updated_history.field_value == 'COOKING'
assert updated_history.date_created is not None

Management Commands

django-field-history comes with a few management commands.

createinitialfieldhistory

This command will inspect all of the models in your application and create FieldHistory objects for the models that have a FieldHistoryTracker. Run this the first time you install django-field-history.

python manage.py createinitialfieldhistory

renamefieldhistory

Use this command after changing a model field name of a field you track with FieldHistoryTracker:

python manage.py renamefieldhistory --model=app_label.model_name --from_field=old_field_name --to_field=new_field_name

For instance, if you have this model:

class Person(models.Model):
    username = models.CharField(max_length=255)

    field_history = FieldHistoryTracker(['username'])

And you change the username field name to handle:

class Person(models.Model):
    handle = models.CharField(max_length=255)

    field_history = FieldHistoryTracker(['handle'])

You will need to also update the field_name value in all FieldHistory objects that point to this model:

python manage.py renamefieldhistory --model=myapp.Person --from_field=username --to_field=handle

Storing Which User Changed the Field

There are two ways to store the user that changed your model field. The simplest way is to use the logged in user that made the request. To do this, add the FieldHistoryMiddleware class to your MIDDLEWARE setting.

MIDDLEWARE = [
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'field_history.middleware.FieldHistoryMiddleware',
]

Alternatively, you can add a _field_history_user property to the model that has fields you are tracking. This property should return the user you would like stored on FieldHistory when your field is updated.

class Pizza(models.Model):
    name = models.CharField(max_length=255)
    updated_by = models.ForeignKey('auth.User')

    field_history = FieldHistoryTracker(['name'])

    @property
    def _field_history_user(self):
        return self.updated_by

Working with MySQL

If you're using MySQL, the default configuration will throw an exception when you run migrations. (By default, FieldHistory.object_id is implemented as a TextField for flexibility, but indexed columns in MySQL InnoDB tables may be a maximum of 767 bytes.) To fix this, you can set FIELD_HISTORY_OBJECT_ID_TYPE in settings.py to override the default field type with one that meets MySQL's constraints. FIELD_HISTORY_OBJECT_ID_TYPE may be set to either:

1. the Django model field class you wish to use, or
2. a tuple (field_class, kwargs), where field_class is a Django model field class and kwargs is a dict of arguments to pass to the field class constructor.

To approximate the default behavior for Postgres when using MySQL, configure object_id to use a CharField by adding the following to settings.py:

from django.db import models
FIELD_HISTORY_OBJECT_ID_TYPE = (models.CharField, {'max_length': 100})

FIELD_HISTORY_OBJECT_ID_TYPE also allows you to use a field type that's more efficient for your use case, even if you're using Postgres (or a similarly unconstrained database). For example, if you always let Django auto-create an id field (implemented internally as an AutoField), setting FIELD_HISTORY_OBJECT_ID_TYPE to IntegerField will result in efficiency gains (both in time and space). This would look like:

from django.db import models
FIELD_HISTORY_OBJECT_ID_TYPE = models.IntegerField

Running Tests

Does the code actually work?

source <YOURVIRTUALENV>/bin/activate
(myenv) $ pip install -r requirements-test.txt
(myenv) $ python runtests.py