在开发机器上进行迁移，没有数据库实例

Question

我在我的开发机器上工作。该代码在 docker 容器中的开发过程中进行了测试，因为：

• 我有一个不错的 docker-compose.yml
• 我想在尽可能类似于部署环境的环境中开发
• 我不想在系统范围内安装任何包（特别是postgres）：我只想在我的开发机器中应用程序进行开发，而不是用于测试或运行应用程序。

现在我正在尝试更新我的迁移：

» DJANGO_SECRET_KEY=xxx python manage.py makemigrations
....
django.db.utils.OperationalError: could not translate host name "postgres" to address: No address associated with hostname

嗯，是的，当然，我的主机看不到postgres容器（只有正在运行的容器才能看到彼此，按照 docker compose 架构）

我可以连接到应用程序容器，在那里进行迁移，并将迁移检索到我的开发机器，但这似乎不是一个好的解决方案。

我的理解是迁移的计算基于：

• 当前存储的迁移，在开发仓库中
• 与这些迁移相比，模型的变化

我不明白为什么我需要一个数据库实例来进行迁移。

我可以在没有连接到数据库的情况下进行迁移吗？如何？

编辑

在下面添加完整的回溯。据我所知，vanillamakemigrations命令尝试连接到数据库。为什么会这样？

我在跑步：

» python
Python 3.6.4 (default, Feb 22 2018, 09:26:37) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import django
>>> django.__version__
'2.0.4'
>>> 


/myvenv/lib/python3.6/site-packages/psycopg2/__init__.py:144: UserWarning: The psycopg2 wheel package will be renamed from release 2.8; in order to keep installing from binary please use "pip install psycopg2-binary" instead. For details see: <http://initd.org/psycopg/docs/install.html#binary-install-from-pypi>.
  """)
Traceback (most recent call last):
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
    self.connect()
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 194, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/postgresql/base.py", line 168, in get_new_connection
    connection = Database.connect(**conn_params)
  File "/myvenv/lib/python3.6/site-packages/psycopg2/__init__.py", line 130, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
psycopg2.OperationalError: could not translate host name "postgres" to address: No address associated with hostname


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

Traceback (most recent call last):
  File "manage.py", line 24, in <module>
    execute_from_command_line(sys.argv)
  File "/myvenv/lib/python3.6/site-packages/django/core/management/__init__.py", line 371, in execute_from_command_line
    utility.execute()
  File "/myvenv/lib/python3.6/site-packages/django/core/management/__init__.py", line 365, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/myvenv/lib/python3.6/site-packages/django/core/management/base.py", line 288, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/myvenv/lib/python3.6/site-packages/django/core/management/base.py", line 335, in execute
    output = self.handle(*args, **options)
  File "/myvenv/lib/python3.6/site-packages/django/core/management/commands/makemigrations.py", line 92, in handle
    loader.check_consistent_history(connection)
  File "/myvenv/lib/python3.6/site-packages/django/db/migrations/loader.py", line 275, in check_consistent_history
    applied = recorder.applied_migrations()
  File "/myvenv/lib/python3.6/site-packages/django/db/migrations/recorder.py", line 61, in applied_migrations
    if self.has_table():
  File "/myvenv/lib/python3.6/site-packages/django/db/migrations/recorder.py", line 44, in has_table
    return self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor())
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 255, in cursor
    return self._cursor()
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 232, in _cursor
    self.ensure_connection()
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
    self.connect()
  File "/myvenv/lib/python3.6/site-packages/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 216, in ensure_connection
    self.connect()
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/base/base.py", line 194, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/myvenv/lib/python3.6/site-packages/django/db/backends/postgresql/base.py", line 168, in get_new_connection
    connection = Database.connect(**conn_params)
  File "/myvenv/lib/python3.6/site-packages/psycopg2/__init__.py", line 130, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
django.db.utils.OperationalError: could not translate host name "postgres" to address: No address associated with hostname

编辑2

从容器运行迁移工作：

root@7dc4a3001a46:/code# python manage.py makemigrations
Migrations for 'something':
  proj/something/migrations/0001_initial.py
    - Create model Something

现在我必须从容器中迁移到我的代码库？多麻烦啊！？我也可以在我的主机上运行数据库，或者允许从开发主机连接到容器化数据库。

我仍然不清楚为什么我需要一个数据库连接来准备迁移。

Answer 1

该makemigrations命令正在尝试访问数据库以检查迁移的一致性。

Ticket 26930建议您可以通过更改设置以使用dummy后端来避免检查。

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.dummy',
    }
}