使用多个数据库的Django错误关系“auth_user”不存在

Question

我正在使用多个数据库（在同一个postgresql数据库中使用不同的模式）处理Django1.9和python 3.3项目。当我第一次尝试迁移项目时，我得到了这个错误

Running migrations:
  Rendering model states... DONE
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying MyApp.0001_initial...Traceback (most recent call last):
  File "/usr/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.ProgrammingError: ERROR:  relation "auth_user" does not exist


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "manage.py", line 10, in 
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3.4/site-packages/django/core/management/__init__.py", line 350, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3.4/site-packages/django/core/management/__init__.py", line 342, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python3.4/site-packages/django/core/management/base.py", line 348, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/lib/python3.4/site-packages/django/core/management/base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 200, in handle
    executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.4/site-packages/django/db/migrations/executor.py", line 92, in migrate
    self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.4/site-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.4/site-packages/django/db/migrations/executor.py", line 198, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/usr/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 90, in __exit__
    self.execute(sql)
  File "/usr/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 110, in execute
    cursor.execute(sql, params)
  File "/usr/lib/python3.4/site-packages/django/db/backends/utils.py", line 79, in execute
    return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
  File "/usr/lib/python3.4/site-packages/django/db/utils.py", line 95, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/lib/python3.4/site-packages/django/utils/six.py", line 685, in reraise
    raise value.with_traceback(tb)
  File "/usr/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: ERROR:  relation "auth_user" does not exist

当auth_user表未迁移时，此错误似乎会在其他项目中出现。在我的例子中，在迁移需要的应用程序之前，用manage.py迁移auth开始迁移并不能解决问题。

迁移过程是否在与我的应用程序数据库相同的数据库中查找auth_user表？是绝对不同的东西吗？

Answer 1

它实际上是一个跨数据库引用问题。Django不能创建跨数据库外键。

来自Django1.8文档（在下一个版本中没有任何解决方案（当前版本是1.10））：

Django目前不支持外键或跨多个数据库的多对多关系。如果使用路由器将模型划分到不同的数据库，则由这些模型定义的任何外键和多对多关系都必须是单个数据库的内部关系。

如果在InnoDB中使用Postgres、Oracle或MySQL，这将在数据库完整性级别强制执行--数据库级别的密钥约束防止创建无法验证的关系。

但是，如果将SQLite或MySQL与MyISAM表一起使用，则没有强制的引用完整性；因此，您可能会“伪造”跨数据库外键。但是，Django并不正式支持这种配置

在我的例子中，因为路由器正在工作，所以有一点小技巧来简化跨数据库对象。

class CrossDBUser(models.Model):
    user = models.IntegerField()

    def get_user(self):
        return User.objects.get(id=self.user)

    def set_user(self, user):
        self.user = user.id

class MyClassWithCrossDB(CrossDBUser):
    field1 = models.CharField(max_length=200, blank=False)
    field2 = models.IntegerField(default=0)

当然，它并不完美，因为它不允许像on_delete=models.cascade这样的自动化操作，而且我不得不使用方法而不是实例变量。但这是一个变通的解决方案。