76 lines
2.5 KiB
ReStructuredText
76 lines
2.5 KiB
ReStructuredText
Migrating existing models to polymorphic
|
|
========================================
|
|
|
|
Existing models can be migrated to become polymorphic models.
|
|
During the migrating, the ``polymorphic_ctype`` field needs to be filled in.
|
|
|
|
This can be done in the following steps:
|
|
|
|
#. Inherit your model from :class:`~polymorphic.models.PolymorphicModel`.
|
|
#. Create a Django migration file to create the ``polymorphic_ctype_id`` database column.
|
|
#. Make sure the proper :class:`~django.contrib.contenttypes.models.ContentType` value is filled in.
|
|
|
|
Filling the content type value
|
|
------------------------------
|
|
|
|
The following Python code can be used to fill the value of a model:
|
|
|
|
.. code-block:: python
|
|
|
|
from django.contrib.contenttypes.models import ContentType
|
|
from myapp.models import MyModel
|
|
|
|
new_ct = ContentType.objects.get_for_model(MyModel)
|
|
MyModel.objects.filter(polymorphic_ctype__isnull=True).update(polymorphic_ctype=new_ct)
|
|
|
|
The creation and update of the ``polymorphic_ctype_id`` column
|
|
can be included in a single Django migration. For example:
|
|
|
|
.. code-block:: python
|
|
|
|
# -*- coding: utf-8 -*-
|
|
from __future__ import unicode_literals
|
|
from django.db import migrations, models
|
|
|
|
|
|
def forwards_func(apps, schema_editor):
|
|
MyModel = apps.get_model('myapp', 'MyModel')
|
|
ContentType = apps.get_model('contenttypes', 'ContentType')
|
|
|
|
new_ct = ContentType.objects.get_for_model(MyModel)
|
|
MyModel.objects.filter(polymorphic_ctype__isnull=True).update(polymorphic_ctype=new_ct)
|
|
|
|
|
|
class Migration(migrations.Migration):
|
|
|
|
dependencies = [
|
|
('contenttypes', '0001_initial'),
|
|
('myapp', '0001_initial'),
|
|
]
|
|
|
|
operations = [
|
|
migrations.AddField(
|
|
model_name='mymodel',
|
|
name='polymorphic_ctype',
|
|
field=models.ForeignKey(related_name='polymorphic_myapp.mymodel_set+', editable=False, to='contenttypes.ContentType', null=True),
|
|
),
|
|
migrations.RunPython(forwards_func, migrations.RunPython.noop),
|
|
]
|
|
|
|
It's recommended to let ``makemigrations`` create the migration file,
|
|
and include the ``RunPython`` manually before running the migration.
|
|
|
|
.. versionadded:: 1.1
|
|
|
|
When the model is created elsewhere, you can also use
|
|
the :func:`polymorphic.utils.reset_polymorphic_ctype` function:
|
|
|
|
.. code-block:: python
|
|
|
|
from polymorphic.utils import reset_polymorphic_ctype
|
|
from myapp.models import Base, Sub1, Sub2
|
|
|
|
reset_polymorphic_ctype(Base, Sub1, Sub2)
|
|
|
|
reset_polymorphic_ctype(Base, Sub1, Sub2, ignore_existing=True)
|