#24434: Django Custom Field inherits ForeignKey deconstruct() fails
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Reporter: greenbender | Owner: nobody
Type: Uncategorized | Status: new
Component: Uncategorized | Version: 1.7
Severity: Normal | Keywords: deconstruct,migration
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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When creating a custom field that inherits from ForeignKey and sets the to
field there are issues with deconstruction.
Simplified example (models.py)
{{{
from django.db import models
from django.contrib.auth.models import User
class UserField(models.ForeignKey):
def __init__(self, *args, **kwargs):
kwargs['to'] = User
super(UserField, self).__init__(*args, **kwargs)
def deconstruct(self):
name, path, args, kwargs = super(UserField, self).deconstruct()
del kwargs['to']
return name, path, args, kwargs
class FooBar(models.Model):
user = UserField()
}}}
When {{{python manage.py makemigrations}}} is run the following exception
is raised.
{{{
Traceback (most recent call last):
File "manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/usr/local/lib/python2.7/dist-
packages/django/core/management/__init__.py", line 385, in
execute_from_command_line
utility.execute()
File "/usr/local/lib/python2.7/dist-
packages/django/core/management/__init__.py", line 377, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/local/lib/python2.7/dist-
packages/django/core/management/base.py", line 288, in run_from_argv
self.execute(*args, **options.__dict__)
File "/usr/local/lib/python2.7/dist-
packages/django/core/management/base.py", line 338, in execute
output = self.handle(*args, **options)
File "/usr/local/lib/python2.7/dist-
packages/django/core/management/commands/makemigrations.py", line 111, in
handle
convert_apps=app_labels or None,
File "/usr/local/lib/python2.7/dist-
packages/django/db/migrations/autodetector.py", line 40, in changes
changes = self._detect_changes(convert_apps, graph)
File "/usr/local/lib/python2.7/dist-
packages/django/db/migrations/autodetector.py", line 139, in
_detect_changes
self.generate_renamed_models()
File "/usr/local/lib/python2.7/dist-
packages/django/db/migrations/autodetector.py", line 413, in
generate_renamed_models
model_fields_def =
self.only_relation_agnostic_fields(model_state.fields)
File "/usr/local/lib/python2.7/dist-
packages/django/db/migrations/autodetector.py", line 79, in
only_relation_agnostic_fields
del deconstruction[2]['to']
KeyError: u'to'
}}}
It can be resolved by not removing the 'to' kwarg during deconstruction,
however, this obviously leaves the unrequired 'to' kwarg in the
constructor, as follows:
{{{
from django.db import models, migrations
from django.conf import settings
import bar.models
class Migration(migrations.Migration):
dependencies = [
migrations.swappable_dependency(settings.AUTH_USER_MODEL),
]
operations = [
migrations.CreateModel(
name='FooBar',
fields=[
('id', models.AutoField(verbose_name='ID',
serialize=False, auto_created=True, primary_key=True)),
('user',
bar.models.UserField(to=settings.AUTH_USER_MODEL)),
],
options={
},
bases=(models.Model,),
),
]
}}}
I've tried a few variations on this (such as supplying User as the first
arg to the super call), however, the result is much the same or creates
additional problems.
The solution proposed at ticket:22263 may solve this problem.
--
Ticket URL: <https://code.djangoproject.com/ticket/24434>
Django <https://code.djangoproject.com/>
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