Bulk Creating and Queryset Updating¶
django-simple-history functions by saving history using a
every time that an object with history is saved. However, for certain bulk
operations, such as bulk_create, bulk_update, and queryset updates,
signals are not sent, and the history is not saved automatically. However,
django-simple-history provides utility functions to work around this.
Bulk Creating a Model with History¶
django-simple-history 2.2.0, we can use the utility function
bulk_create_with_history in order to bulk create objects while saving their
>>> from simple_history.utils import bulk_create_with_history >>> from simple_history.tests.models import Poll >>> from django.utils.timezone import now >>> >>> data = [Poll(id=x, question='Question ' + str(x), pub_date=now()) for x in range(1000)] >>> objs = bulk_create_with_history(data, Poll, batch_size=500) >>> Poll.objects.count() 1000 >>> Poll.history.count() 1000
If you want to specify a change reason or history user for each record in the bulk create, you can add _change_reason or _history_user on each instance:
>>> for poll in data: poll._change_reason = 'reason' poll._history_user = my_user >>> objs = bulk_create_with_history(data, Poll, batch_size=500) >>> Poll.history.get(id=data.id).history_change_reason 'reason'
You can also specify a default user or default change reason responsible for the change (_history_user and _change_reason take precedence).
>>> user = User.objects.create_user("tester", "firstname.lastname@example.org") >>> objs = bulk_create_with_history(data, Poll, batch_size=500, default_user=user) >>> Poll.history.get(id=data.id).history_user == user True
Bulk Updating a Model with History (New)¶
Bulk update was introduced with Django 2.2. We can use the utility function
bulk_update_with_history in order to bulk update objects using Django’s
bulk_update function while saving the object history:
>>> from simple_history.utils import bulk_create_with_history >>> from simple_history.tests.models import Poll >>> from django.utils.timezone import now >>> >>> data = [Poll(id=x, question='Question ' + str(x), pub_date=now()) for x in range(1000)] >>> objs = bulk_create_with_history(data, Poll, batch_size=500) >>> for obj in objs: obj.question = 'Duplicate Questions' >>> bulk_update_with_history(objs, Poll, ['question'], batch_size=500) >>> Poll.objects.first().question 'Duplicate Question'
QuerySet Updates with History (Updated in Django 2.2)¶
bulk_create, queryset updates perform an SQL update query on
the queryset, and never return the actual updated objects (which would be
necessary for the inserts into the historical table). Thus, we tell you that
queryset updates will not save history (since no
post_save signal is sent).
As the Django documentation says:
If you want to update a bunch of records for a model that has a custom ``save()`` method, loop over them and call ``save()``, like this:
for e in Entry.objects.filter(pub_date__year=2010): e.comments_on = False e.save()
Note: Django 2.2 now allows
post_save signals are sent still.
Tracking Custom Users¶
ERRORS: custom_user.HistoricalCustomUser.history_user: (fields.E300) Field defines a relation with model 'custom_user.CustomUser', which is either not installed, or is abstract.
register()to track changes to the custom user model instead of setting
HistoricalRecordson the model directly.
The reason for this, is that unfortunately
HistoricalRecordscannot be set directly on a swapped user model because of the user foreign key to track the user making changes.
Using django-webtest with Middleware¶
When using django-webtest to test your Django project with the django-simple-history middleware, you may run into an error similar to the following:
django.db.utils.IntegrityError: (1452, 'Cannot add or update a child row: a foreign key constraint fails (`test_env`.`core_historicaladdress`, CONSTRAINT `core_historicaladdress_history_user_id_0f2bed02_fk_user_user_id` FOREIGN KEY (`history_user_id`) REFERENCES `user_user` (`id`))')
This error occurs because
DEBUG_PROPAGATE_EXCEPTIONS to true preventing the middleware from cleaning
up the request. To solve this issue, add the following code to any
tearDown method that
from simple_history.middleware import HistoricalRecords if hasattr(HistoricalRecords.thread, 'request'): del HistoricalRecords.thread.request
Using F() expressions¶
F() expressions, as described here, do not work on models that have
history. Simple history inserts a new record in the historical table for any
model being updated. However,
F() expressions are only functional on updates.
Thus, when an
F() expression is used on a model with a history table, the
historical model tries to insert using the
F() expression, and raises a
Reserved Field Names¶
For each base model that has its history tracked using
an associated historical model is created. Thus, if we have:
class BaseModel(models.Model): history = HistoricalRecords()
a Django model called
HistoricalBaseModel is also created with all of the fields
BaseModel, plus a few extra fields and methods that are on all historical models.
Since these fields and methods are on all historical models, any field or method names on a base model that clash with those names will not be on the historical model (and, thus, won’t be tracked). The reserved historical field and method names are below:
So if we have:
class BaseModel(models.Model): instance = models.CharField(max_length=255) history = HistoricalRecords()
instance field will not actually be tracked on the history table because it’s
in the reserved set of terms.
django-simple-history supports tracking history on models that use multi-table
inheritance, such as:
class ParentModel(models.Model): parent_field = models.CharField(max_length=255) history = HistoricalRecords() class ChildModel(ParentModel): child_field = models.CharField(max_length=255) history = HistoricalRecords()
A few notes:
On the child model, the
HistoricalRecordsinstance is not inherited from the parent model. This means that you can choose to track changes on just the parent model, just the child model, or both.
The child’s history table contains all fields from the child model as well as all the fields from the parent model.
Updating a child instance only updates the child’s history table, not the parent’s history table.
Usage with django-modeltranslation¶
If you have
django-modeltranslation installed, you will need to use the
method to model translation, as described here.
Pointing to the model¶
Sometimes you have to point to the model of the historical records. Examples are Django’s generic views or Django REST framework’s serializers. You can get there through your HistoricalRecords manager you defined in your model. According to our example:
class PollHistoryListView(ListView): # or PollHistorySerializer(ModelSerializer): class Meta: model = Poll.history.model # ...
Working with BitBucket Pipelines¶
When using BitBucket Pipelines to test your Django project with the
django-simple-history middleware, you will run into an error relating to missing migrations relating to the historic User model from the auth app. This is because the migration file is not held within either your project or django-simple-history. In order to pypass the error you need to add a
`python manage.py makemigrations auth` step into your YML file prior to running the tests.