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