Django 迁移失败，显示“__fake__.DoesNotExist：权限匹配查询不存在。”
Django migration fails with "__fake__.DoesNotExist: Permission matching query does not exist."
在 Django 1.8 项目中，我有一个运行良好的迁移，when it had the following code:
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import migrations
from django.conf import settings
def update_site_forward(apps, schema_editor):
"""Add group osmaxx."""
Group = apps.get_model("auth", "Group")
Group.objects.create(name=settings.OSMAXX_FRONTEND_USER_GROUP)
def update_site_backward(apps, schema_editor):
"""Revert add group osmaxx."""
Group = apps.get_model("auth", "Group")
Group.objects.get(name=settings.OSMAXX_FRONTEND_USER_GROUP).delete()
class Migration(migrations.Migration):
dependencies = [
('auth', '0001_initial'),
]
operations = [
migrations.RunPython(update_site_forward, update_site_backward),
]
此组是在迁移中创建的，因为它应在 Web 应用程序的所有安装中可用。为了让它更有用，我想也给它一个默认权限，所以我把 update_site_forward 改成了：
def update_site_forward(apps, schema_editor):
"""Add group osmaxx."""
Group = apps.get_model("auth", "Group")
Permission = apps.get_model("auth", "Permission")
ContentType = apps.get_model("contenttypes", "ContentType")
ExtractionOrder = apps.get_model("excerptexport", "ExtractionOrder")
group = Group.objects.create(name=settings.OSMAXX_FRONTEND_USER_GROUP)
content_type = ContentType.objects.get_for_model(ExtractionOrder)
permission = Permission.objects.get(codename='add_extractionorder',
content_type=content_type) # line 16
group.permissions.add(permission)
和Migration.dependencies到：
dependencies = [
('contenttypes', '0002_remove_content_type_name'),
('excerptexport', '0001_initial'),
('auth', '0001_initial'),
]
虽然应用迁移（在首先还原它之后）(python3 manage.py migrate auth 0001 && python3 managy.py migrate) 有效，但使用此迁移和所有其他迁移 (python3 manage.py migrate) 迁移新创建的 PostgreSQL 数据库失败：
Operations to perform:
Synchronize unmigrated apps: debug_toolbar, django_extensions, messages, humanize, social_auth, kombu_transport_django, staticfiles
Apply all migrations: excerptexport, admin, sites, contenttypes, sessions, default, stored_messages, auth
Synchronizing apps without migrations:
Creating tables...
Running deferred SQL...
Installing custom SQL...
Running migrations:
Rendering model states... DONE
Applying auth.0002_add_default_usergroup_osmaxx...Traceback (most recent call last):
File "manage.py", line 17, in <module>
execute_from_command_line(sys.argv)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
utility.execute()
File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 330, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 393, in run_from_argv
self.execute(*args, **cmd_options)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 444, in execute
output = self.handle(*args, **options)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/commands/migrate.py", line 221, in handle
executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 110, in migrate
self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 148, in apply_migration
state = migration.apply(state, schema_editor)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/migration.py", line 115, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/operations/special.py", line 183, in database_forwards
self.code(from_state.apps, schema_editor)
File "/home/osmaxx/source/osmaxx/contrib/auth/migrations/0002_add_default_usergroup_osmaxx.py", line 16, in update_site_forward
permission = Permission.objects.get(codename='add_extractionorder', content_type=content_type)
File "/usr/local/lib/python3.4/dist-packages/django/db/models/manager.py", line 127, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/usr/local/lib/python3.4/dist-packages/django/db/models/query.py", line 334, in get
self.model._meta.object_name
__fake__.DoesNotExist: Permission matching query does not exist.
我做错了什么？
默认权限是在 post_migrate 信号处理程序中创建的，在 迁移 运行 之后。如果您更新的代码 运行 作为第二个 manage.py migrate 运行 的一部分，这将不是问题，但在测试套件和任何新部署中它是一个问题。
简单的解决方法是更改此行：
permission = Permission.objects.get(codename='add_extractionorder',
content_type=content_type) # line 16
对此：
permission, created = Permission.objects.get_or_create(codename='add_extractionorder',
content_type=content_type)
创建默认权限的信号处理程序永远不会创建重复的权限，因此如果它不存在则创建它是安全的。
在 Django 1.8 项目中，我有一个运行良好的迁移，when it had the following code:
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import migrations
from django.conf import settings
def update_site_forward(apps, schema_editor):
"""Add group osmaxx."""
Group = apps.get_model("auth", "Group")
Group.objects.create(name=settings.OSMAXX_FRONTEND_USER_GROUP)
def update_site_backward(apps, schema_editor):
"""Revert add group osmaxx."""
Group = apps.get_model("auth", "Group")
Group.objects.get(name=settings.OSMAXX_FRONTEND_USER_GROUP).delete()
class Migration(migrations.Migration):
dependencies = [
('auth', '0001_initial'),
]
operations = [
migrations.RunPython(update_site_forward, update_site_backward),
]
此组是在迁移中创建的，因为它应在 Web 应用程序的所有安装中可用。为了让它更有用，我想也给它一个默认权限，所以我把 update_site_forward 改成了：
def update_site_forward(apps, schema_editor):
"""Add group osmaxx."""
Group = apps.get_model("auth", "Group")
Permission = apps.get_model("auth", "Permission")
ContentType = apps.get_model("contenttypes", "ContentType")
ExtractionOrder = apps.get_model("excerptexport", "ExtractionOrder")
group = Group.objects.create(name=settings.OSMAXX_FRONTEND_USER_GROUP)
content_type = ContentType.objects.get_for_model(ExtractionOrder)
permission = Permission.objects.get(codename='add_extractionorder',
content_type=content_type) # line 16
group.permissions.add(permission)
和Migration.dependencies到：
dependencies = [
('contenttypes', '0002_remove_content_type_name'),
('excerptexport', '0001_initial'),
('auth', '0001_initial'),
]
虽然应用迁移（在首先还原它之后）(python3 manage.py migrate auth 0001 && python3 managy.py migrate) 有效，但使用此迁移和所有其他迁移 (python3 manage.py migrate) 迁移新创建的 PostgreSQL 数据库失败：
Operations to perform:
Synchronize unmigrated apps: debug_toolbar, django_extensions, messages, humanize, social_auth, kombu_transport_django, staticfiles
Apply all migrations: excerptexport, admin, sites, contenttypes, sessions, default, stored_messages, auth
Synchronizing apps without migrations:
Creating tables...
Running deferred SQL...
Installing custom SQL...
Running migrations:
Rendering model states... DONE
Applying auth.0002_add_default_usergroup_osmaxx...Traceback (most recent call last):
File "manage.py", line 17, in <module>
execute_from_command_line(sys.argv)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
utility.execute()
File "/usr/local/lib/python3.4/dist-packages/django/core/management/__init__.py", line 330, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 393, in run_from_argv
self.execute(*args, **cmd_options)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/base.py", line 444, in execute
output = self.handle(*args, **options)
File "/usr/local/lib/python3.4/dist-packages/django/core/management/commands/migrate.py", line 221, in handle
executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 110, in migrate
self.apply_migration(states[migration], migration, fake=fake, fake_initial=fake_initial)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/executor.py", line 148, in apply_migration
state = migration.apply(state, schema_editor)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/migration.py", line 115, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/usr/local/lib/python3.4/dist-packages/django/db/migrations/operations/special.py", line 183, in database_forwards
self.code(from_state.apps, schema_editor)
File "/home/osmaxx/source/osmaxx/contrib/auth/migrations/0002_add_default_usergroup_osmaxx.py", line 16, in update_site_forward
permission = Permission.objects.get(codename='add_extractionorder', content_type=content_type)
File "/usr/local/lib/python3.4/dist-packages/django/db/models/manager.py", line 127, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/usr/local/lib/python3.4/dist-packages/django/db/models/query.py", line 334, in get
self.model._meta.object_name
__fake__.DoesNotExist: Permission matching query does not exist.
我做错了什么？
默认权限是在 post_migrate 信号处理程序中创建的，在 迁移 运行 之后。如果您更新的代码 运行 作为第二个 manage.py migrate 运行 的一部分，这将不是问题，但在测试套件和任何新部署中它是一个问题。
简单的解决方法是更改此行：
permission = Permission.objects.get(codename='add_extractionorder',
content_type=content_type) # line 16
对此：
permission, created = Permission.objects.get_or_create(codename='add_extractionorder',
content_type=content_type)
创建默认权限的信号处理程序永远不会创建重复的权限，因此如果它不存在则创建它是安全的。