Common Issues¶
Bulk Creating and Queryset Updating¶
django-simple-history
functions by saving history using a post_save
signal
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¶
As of 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
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)
>>> 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[0].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", "tester@example.com")
>>> objs = bulk_create_with_history(data, Poll, batch_size=500, default_user=user)
>>> Poll.history.get(id=data[0].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)¶
Unlike with 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 bulk_update
. No pre_save
or post_save
signals are sent still.
Tracking Custom Users¶
fields.E300
: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.
Use
register()
to track changes to the custom user model instead of settingHistoricalRecords
on the model directly.The reason for this, is that unfortunately
HistoricalRecords
cannot 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 django-webtest
sets
DEBUG_PROPAGATE_EXCEPTIONS
to true preventing the middleware from cleaning
up the request. To solve this issue, add the following code to any
clean_environment
or tearDown
method that
you use:
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
ValueError
.
Reserved Field Names¶
For each base model that has its history tracked using django-simple-history
,
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
from 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:
history_id
history_date
history_change_reason
history_type
history_object
history_user
history_user_id
instance
instance_type
next_record
prev_record
revert_url
__str__
So if we have:
class BaseModel(models.Model):
instance = models.CharField(max_length=255)
history = HistoricalRecords()
the instance
field will not actually be tracked on the history table because it’s
in the reserved set of terms.
Multi-table Inheritance¶
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
HistoricalRecords
instance 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 register()
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.