Loading AUTHORS +1 −0 Original line number Diff line number Diff line Loading @@ -700,6 +700,7 @@ answer newbie questions, and generally made Django that much better: Tim Graham <timograham@gmail.com> Tim Heap <tim@timheap.me> Tim Saylor <tim.saylor@gmail.com> Tobias Kunze <rixx@cutebit.de> Tobias McNulty <http://www.caktusgroup.com/blog> tobias@neuyork.de Todd O'Bryan <toddobryan@mac.com> Loading docs/howto/writing-migrations.txt +51 −0 Original line number Diff line number Diff line Loading @@ -226,3 +226,54 @@ Prefer using ``dependencies`` over ``run_before`` when possible. You should only use ``run_before`` if it is undesirable or impractical to specify ``dependencies`` in the migration which you want to run after the one you are writing. Migrating data between third-party apps ======================================= You can use a data migration to move data from one third-party application to another. If you plan to remove the old app later, you'll need to set the ``dependencies`` property based on whether or not the old app is installed. Otherwise, you'll have missing dependencies once you uninstall the old app. Similarly, you'll need to catch :exc:`LookupError` in the ``apps.get_model()`` call that retrieves models from the old app. This approach allows you to deploy your project anywhere without first installing and then uninstalling the old app. Here's a sample migration: .. snippet:: :filename: myapp/migrations/0124_move_old_app_to_new_app.py from django.apps import apps as global_apps from django.db import migrations def forwards(apps, schema_editor): try: OldModel = apps.get_model('old_app', 'OldModel') except LookupError: # The old app isn't installed. return NewModel = apps.get_model('new_app', 'NewModel') NewModel.objects.bulk_create( NewModel(new_attribute=old_object.old_attribute) for old_object in OldModel.objects.all() ) class Migration(migrations.Migration): operations = [ migrations.RunPython(forwards, migrations.RunPython.noop), ] dependencies = [ ('myapp', '0123_the_previous_migration'), ('new_app', '0001_initial'), ] if global_apps.is_installed('old_app'): dependencies.append(('old_app', '0001_initial')) Also consider what you want to happen when the migration is unapplied. You could either do nothing (as in the example above) or remove some or all of the data from the new application. Adjust the second argument of the :mod:`~django.db.migrations.operations.RunPython` operation accordingly. Loading
AUTHORS +1 −0 Original line number Diff line number Diff line Loading @@ -700,6 +700,7 @@ answer newbie questions, and generally made Django that much better: Tim Graham <timograham@gmail.com> Tim Heap <tim@timheap.me> Tim Saylor <tim.saylor@gmail.com> Tobias Kunze <rixx@cutebit.de> Tobias McNulty <http://www.caktusgroup.com/blog> tobias@neuyork.de Todd O'Bryan <toddobryan@mac.com> Loading
docs/howto/writing-migrations.txt +51 −0 Original line number Diff line number Diff line Loading @@ -226,3 +226,54 @@ Prefer using ``dependencies`` over ``run_before`` when possible. You should only use ``run_before`` if it is undesirable or impractical to specify ``dependencies`` in the migration which you want to run after the one you are writing. Migrating data between third-party apps ======================================= You can use a data migration to move data from one third-party application to another. If you plan to remove the old app later, you'll need to set the ``dependencies`` property based on whether or not the old app is installed. Otherwise, you'll have missing dependencies once you uninstall the old app. Similarly, you'll need to catch :exc:`LookupError` in the ``apps.get_model()`` call that retrieves models from the old app. This approach allows you to deploy your project anywhere without first installing and then uninstalling the old app. Here's a sample migration: .. snippet:: :filename: myapp/migrations/0124_move_old_app_to_new_app.py from django.apps import apps as global_apps from django.db import migrations def forwards(apps, schema_editor): try: OldModel = apps.get_model('old_app', 'OldModel') except LookupError: # The old app isn't installed. return NewModel = apps.get_model('new_app', 'NewModel') NewModel.objects.bulk_create( NewModel(new_attribute=old_object.old_attribute) for old_object in OldModel.objects.all() ) class Migration(migrations.Migration): operations = [ migrations.RunPython(forwards, migrations.RunPython.noop), ] dependencies = [ ('myapp', '0123_the_previous_migration'), ('new_app', '0001_initial'), ] if global_apps.is_installed('old_app'): dependencies.append(('old_app', '0001_initial')) Also consider what you want to happen when the migration is unapplied. You could either do nothing (as in the example above) or remove some or all of the data from the new application. Adjust the second argument of the :mod:`~django.db.migrations.operations.RunPython` operation accordingly.
