#27941: Incorrect checking or re-conciliation of parent/child fields when
inheritance is changed to abstract
-------------------------------------+-------------------------------------
Reporter: Sawan | Owner: nobody
Vithlani |
Type: | Status: new
Uncategorized |
Component: | Version: 1.10
Migrations | Keywords: model abstract
Severity: Normal | inheritance field
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Consider the following class hierarchy:
{{{#!python
class TestCase(models.Model):
name = models.CharField(max_length=10)
class TerminalTest(TestCase):
pass
class BrowserTest(TestCase):
pass
$ ./manage.py makemigrations testbed
Migrations for 'testbed':
testbed\migrations\0001_initial.py:
- Create model TestCase
- Create model BrowserTest
- Create model TerminalTest
$ ./manage.py migrate testbed
Operations to perform:
Apply all migrations: testbed
Running migrations:
Applying testbed.0001_initial... OK
}}}
Now we want to make the parent an abstract class:
{{{#!python
class TestCase(models.Model):
name = models.CharField(max_length=10)
class Meta:
abstract = True
class TerminalTest(TestCase):
pass
class BrowserTest(TestCase):
pass
$ ./manage.py makemigrations testbed
You are trying to add a non-nullable field 'id' to browsertest without a
default; we can't do that (the database needs something to populate
existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a
null value for this column)
2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can
do e.g. timezone.now
Type 'exit' to exit this prompt
>>> 1
You are trying to add a non-nullable field 'name' to browsertest without a
default; we can't do that (the database needs something to populate
existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a
null value for this column)
2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can
do e.g. timezone.now
Type 'exit' to exit this prompt
>>> ' '
You are trying to add a non-nullable field 'id' to terminaltest without a
default; we can't do that (the database needs something to populate
existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a
null value for this column)
2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can
do e.g. timezone.now
Type 'exit' to exit this prompt
>>> 1
You are trying to add a non-nullable field 'name' to terminaltest without
a default; we can't do that (the database needs something to populate
existing rows).
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a
null value for this column)
2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can
do e.g. timezone.now
Type 'exit' to exit this prompt
>>> ' '
Migrations for 'testbed':
testbed\migrations\0002_auto_20170315_1711.py:
- Remove field testcase_ptr from browsertest
- Remove field testcase_ptr from terminaltest
- Add field id to browsertest
- Add field name to browsertest
- Add field id to terminaltest
- Add field name to terminaltest
- Delete model TestCase
}}}
At this point, please assume that bug
#[https://code.djangoproject.com/ticket/27940 27940] has been fixed.
In this case, it was fixed by the following temporary hack in
'**django/db/backends/sqlite3/schema.py** at
''[https://github.com/django/django/blob/320ec4ed27c254a87e09a70601b1b27ae0a0456e/django/db/backends/sqlite3/schema.py#L195-L198
this place:]
{{{#!python
field_maps = list(mapping.items())
query = "INSERT INTO %s (%s) SELECT %s FROM %s" % (
self.quote_name(temp_model._meta.db_table),
', '.join(self.quote_name(x) for x, y in field_maps),
', '.join(y for x, y in field_maps),
self.quote_name(model._meta.db_table),
)
corrected_query= query.replace(' () SELECT FROM ', ' SELECT *
FROM ')
print('\n\t\t Changing: {} \n\t\t To: {} \n'.format(query,
corrected_query))
self.execute(corrected_query)
}}}
Now to run the migration:
{{{#!python
$ ./manage.py migrate testbed
Operations to perform:
Apply all migrations: testbed
Running migrations:
Applying testbed.0002_auto_20170315_1711...
Changing: INSERT INTO "testbed_browsertest" () SELECT
FROM "testbed_browsertest__old"
To: INSERT INTO "testbed_browsertest" SELECT * FROM
"testbed_browsertest__old"
Changing: INSERT INTO "testbed_terminaltest" () SELECT
FROM "testbed_terminaltest__old"
To: INSERT INTO "testbed_terminaltest" SELECT * FROM
"testbed_terminaltest__old"
Traceback (most recent call last):
File "./manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "C:\my-venv\lib\site-packages\django\core\management\__init__.py",
line 367, in execute_from_command_line
utility.execute()
File "C:\my-venv\lib\site-packages\django\core\management\__init__.py",
line 359, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "C:\my-venv\lib\site-packages\django\core\management\base.py", line
294, in run_from_argv
self.execute(*args, **cmd_options)
File "C:\my-venv\lib\site-packages\django\core\management\base.py", line
345, in execute
output = self.handle(*args, **options)
File "C:\my-venv\lib\site-
packages\django\core\management\commands\migrate.py", line 204, in handle
fake_initial=fake_initial,
File "C:\my-venv\lib\site-packages\django\db\migrations\executor.py",
line 115, in migrate
state = self._migrate_all_forwards(state, plan, full_plan, fake=fake,
fake_initial=fake_initial)
File "C:\my-venv\lib\site-packages\django\db\migrations\executor.py",
line 145, in _migrate_all_forwards
state = self.apply_migration(state, migration, fake=fake,
fake_initial=fake_initial)
File "C:\my-venv\lib\site-packages\django\db\migrations\executor.py",
line 244, in apply_migration
state = migration.apply(state, schema_editor)
File "C:\my-venv\lib\site-packages\django\db\migrations\migration.py",
line 119, in apply
operation.state_forwards(self.app_label, project_state)
File "C:\my-venv\lib\site-
packages\django\db\migrations\operations\fields.py", line 73, in
state_forwards
state.reload_model(app_label, self.model_name_lower)
File "C:\my-venv\lib\site-packages\django\db\migrations\state.py", line
162, in reload_model
self.apps.render_multiple(states_to_be_rendered)
File "C:\my-venv\lib\site-packages\django\db\migrations\state.py", line
277, in render_multiple
model.render(self)
File "C:\my-venv\lib\site-packages\django\db\migrations\state.py", line
559, in render
body,
File "C:\my-venv\lib\site-packages\django\db\models\base.py", line 226,
in __new__
base.__name__,
django.core.exceptions.FieldError: Local field 'id' in class 'BrowserTest'
clashes with field of the same name from base class 'TestCase'.
}}}
This seems to happen because some verification code in the
**django.db.models.base.ModelBase' is unable to distinguish or re-concile
between fields in the parent class (**TestCase**, now abstract) and the
child class **BrowserTest**.
This seems to be very strange the clash is on the **'id'** field that
isn't even explicitly defined on the models -- it is auto added by the
system to serve as a primary key.
--
Ticket URL: <https://code.djangoproject.com/ticket/27941>
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