Advanced Usage¶
Version-controlling with South¶
By default, Historical models live in the same app as the model they track. Historical models are tracked by South in the same way as any other model. Whenever the original model changes, the historical model will change also.
Therefore tracking historical models with South should work automatically.
Locating past model instance¶
Two extra methods are provided for locating previous models instances on historical record model managers.
as_of¶
This method will return an instance of the model as it would have existed at the provided date and time.
>>> from datetime import datetime
>>> poll.history.as_of(datetime(2010, 10, 25, 18, 4, 0))
<HistoricalPoll: Poll object as of 2010-10-25 18:03:29.855689>
>>> poll.history.as_of(datetime(2010, 10, 25, 18, 5, 0))
<HistoricalPoll: Poll object as of 2010-10-25 18:04:13.814128>
most_recent¶
This method will return the most recent copy of the model available in the model history.
>>> from datetime import datetime
>>> poll.history.most_recent()
<HistoricalPoll: Poll object as of 2010-10-25 18:04:13.814128>
History for Third-Party Model¶
To track history for a model you didn’t create, use the
simple_history.register
utility. You can use this to track models from
third-party apps you don’t have control over. Here’s an example of using
simple_history.register
to history-track the User
model from the
django.contrib.auth
app:
from simple_history import register
from django.contrib.auth.models import User
register(User)
Recording Which User Changed a Model¶
To denote which user changed a model, assign a _history_user
attribute on
your model.
For example if you have a changed_by
field on your model that records which
user last changed the model, you could create a _history_user
property
referencing the changed_by
field:
from django.db import models
from simple_history.models import HistoricalRecords
class Poll(models.Model):
question = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')
changed_by = models.ForeignKey('auth.User')
history = HistoricalRecords()
@property
def _history_user(self):
return self.changed_by
@_history_user.setter
def _history_user(self, value):
self.changed_by = value
Admin integration requires that you use a _history_user.setter
attribute with your custom _history_user
property (see Integration with Django Admin).
Custom history_date
¶
You’re able to set a custom history_date
attribute for the historical
record, by defining the property _history_date
in your model. That’s
helpful if you want to add versions to your model, which happened before the
current model version, e.g. when batch importing historical data. The content
of the property _history_date
has to be a datetime-object, but setting the
value of the property to a DateTimeField
, which is already defined in the
model, will work too.
from django.db import models
from simple_history.models import HistoricalRecords
class Poll(models.Model):
question = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')
changed_by = models.ForeignKey('auth.User')
history = HistoricalRecords()
__history_date = None
@property
def _history_date(self):
return self.__history_date
@_history_date.setter
def _history_date(self, value):
self.__history_date = value
from datetime import datetime
from models import Poll
my_poll = Poll(question="what's up?")
my_poll._history_date = datetime.now()
my_poll.save()
Change Base Class of HistoricalRecord Models¶
To change the auto-generated HistoricalRecord models base class from
models.Model
, pass in the abstract class in a list to bases
.
class RoutableModel(models.Model):
class Meta:
abstract = True
class Poll(models.Model):
question = models.CharField(max_length=200)
pub_date = models.DateTimeField('date published')
changed_by = models.ForeignKey('auth.User')
history = HistoricalRecords(bases=[RoutableModel])