Django-租户“无法创建django_migrations表”

Question

当我们的生产数据库由于迁移过程中的错误而没有被迁移时，就出现了一个问题。此错误涉及包django-tenants的使用，该包是django-tenant-schemas包的分叉。

错误：

Traceback (most recent call last):
File "/backend/manage.py", line 21, in <module>
    main()
  File "/backend/manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python3.9/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "/usr/local/lib/python3.9/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python3.9/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/local/lib/python3.9/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/usr/local/lib/python3.9/site-packages/django_tenants/management/commands/migrate_schemas.py", line 89, in handle
    executor.run_migrations(tenants=tenants)
  File "/usr/local/lib/python3.9/site-packages/django_tenants/migration_executors/standard.py", line 14, in run_migrations
Starting new HTTPS connection (1): o1380729.ingest.sentry.io:443
    run_migrations(self.args, self.options, self.codename, schema_name, idx=idx, count=len(tenants))
  File "/usr/local/lib/python3.9/site-packages/django_tenants/migration_executors/base.py", line 45, in run_migrations
    migration_recorder.ensure_schema()
  File "/usr/local/lib/python3.9/site-packages/django/db/migrations/recorder.py", line 70, in ensure_schema
    raise MigrationSchemaMissing("Unable to create the django_migrations table (%s)" % exc)
django.db.migrations.exceptions.MigrationSchemaMissing: Unable to create the django_migrations table (relation "django_migrations" already exists
)

是什么导致了这个错误？

Answer 1

在错误发生之前，有几个租户确实迁移了，这一事实告诉您，错误是由特定的租户引起的。要找出错误的来源，我们需要跟踪跟踪。在第二行到最后一行，我们看到：

File "/usr/local/lib/python3.9/site-packages/django_tenants/migration_executors/standard.py", line 14, in run_migrations 
Starting new HTTPS connection (1): o1380729.ingest.sentry.io:443 run_migrations(self.args, self.options, self.codename, schema_name, idx=idx, count=len(tenants)) 
File "/usr/local/lib/python3.9/site-packages/django_tenants/migration_executors/base.py", line 45, in run_migrations migration_recorder.ensure_schema() 
File "/usr/local/lib/python3.9/site-packages/django/db/migrations/recorder.py"

因此，看看django_tenants源代码，在/usr/local/lib/python3.9/site-packages/django_tenants/migration_executors/base.py第45行附近，我们可以看到以下代码：

    connection = connections[options.get('database', get_tenant_database_alias())]
    connection.set_schema(schema_name, tenant_type=tenant_type)

    # ensure that django_migrations table is created in the schema before migrations run, otherwise the migration
    # table in the public schema gets picked and no migrations are applied
    migration_recorder = MigrationRecorder(connection)
    migration_recorder.ensure_schema() # line 45

由于schema_name被传递给connection.set_schema(schema_name, tenant_type=tenant_type)，所以我们可以上一行并放置一个print语句来打印正在迁移的模式的名称。此print语句将在迁移期间显示在控制台上，并显示有问题的架构。在我们的示例中，由于模式名称中大写的不同，允许使用重复的架构名称。

为了使用python manage.py shell更改模式名称，我们使用instance = TenantModel.objects.get(schema_name="conflicting_name")导入租户模型，并使用instance.schema_name("new_name")将模式设置为不同的名称，并在实例上调用instance.save()。

这运行了一个迁移并解决了这个问题！