使用 sqlalchemy、alembic 将列动态添加到现有表

Question

我想动态地将列添加到数据库中的表中，因为我不想在 SQLalchemy 类中设置表时指定所有列

为了解决这个问题，我正在使用 alembic 向表中添加列，但我遇到了问题。

在我的 python 脚本中，我定义了一个类，如下所示。

DATABASE_URL_dev = "postgresql+psycopg2://user:password@localhost:5432/testdb"

engine = create_engine(DATABASE_URL_dev)
Base = declarative_base(engine)


class my_class1(Base):
    __tablename__ = "test1"

    id = Column(Integer, primary_key=True)
    list = Column(String)

def  loadsession():
    Base.metadata.create_all(engine)
    Session = sessionmaker(bind=engine)
    session = Session()
    return session

session = loadsession()

现在我想在数据库中的表 test1 中添加一个新列（“new_column”）。

然后我使用 Alembic 按照https://alembic.sqlalchemy.org/en/latest/tutorial.html 的说明进行了以下操作：

1. 通过运行 pip install alembic 安装了 alembic
2. 使用 alembic init alembic 创建了一个环境
3. 通过在 sqlalchemy.url 输入“postgresql+psycopg2://user:password@localhost:5432/testdb”来编辑 .ini 文件
4. 通过运行 alembic revision -m "add a column" 创建了一个迁移脚本
5. 然后我通过在 upgrade() 中添加以下“op.add_column('test1', sa.Column('new_column', sa.String))”来编辑脚本
6. 使用“alembic 升级头”运行第一次迁移 这给了我以下错误：

Traceback (most recent call last):
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\runpy.py", line 193, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "C:\Users\user\AppData\Local\Programs\Python\Python38-32\Scripts\alembic.exe\__main__.py", line 9, in <module>
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\config.py", line 577, in main
    CommandLine(prog=prog).main(argv=argv)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\config.py", line 571, in main
    self.run_cmd(cfg, options)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\config.py", line 548, in run_cmd
    fn(
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\command.py", line 298, in upgrade
    script.run_env()
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\script\base.py", line 489, in run_env
    util.load_python_file(self.dir, "env.py")
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\util\pyfiles.py", line 98, in load_python_file
    module = load_module_py(module_id, path)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\alembic\util\compat.py", line 184, in load_module_py
    spec.loader.exec_module(module)
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "y\env.py", line 77, in <module>
    run_migrations_online()
  File "y\env.py", line 65, in run_migrations_online
    with connectable.connect() as connection:
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2218, in connect
    return self._connection_cls(self, **kwargs)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 103, in __init__
    else engine.raw_connection()
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2317, in raw_connection
    return self._wrap_pool_connect(
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2288, in _wrap_pool_connect
    Connection._handle_dbapi_exception_noconnection(
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 1554, in _handle_dbapi_exception_noconnection
    util.raise_(
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\util\compat.py", line 178, in raise_
    raise exception
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\base.py", line 2285, in _wrap_pool_connect
    return fn()
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 303, in unique_connection
    return _ConnectionFairy._checkout(self)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 773, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 492, in checkout
    rec = pool._do_get()
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\impl.py", line 238, in _do_get
    return self._create_connection()
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 308, in _create_connection
    return _ConnectionRecord(self)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 437, in __init__
    self.__connect(first_connect_check=True)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 657, in __connect
    pool.logger.debug("Error on connect(): %s", e)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\util\langhelpers.py", line 68, in __exit__
    compat.raise_(
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\util\compat.py", line 178, in raise_
    raise exception
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\pool\base.py", line 652, in __connect
    connection = pool._invoke_creator(self)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\strategies.py", line 114, in connect
    return dialect.connect(*cargs, **cparams)
  File "c:\users\user\appdata\local\programs\python\python38-32\lib\site-packages\sqlalchemy\engine\default.py", line 488, in connect
    return self.dbapi.connect(*cargs, **cparams)
  File "c:\users\c\appdata\local\programs\python\python38-32\lib\site-packages\psycopg2\__init__.py", line 126, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
sqlalchemy.exc.OperationalError: (psycopg2.OperationalError)
(Background on this error at: http://sqlalche.me/e/e3q8)

问题

1. 这是动态添加列的正确方法还是应该以其他方式完成？
2. 如何解决 sqlalchemy 操作错误？

谢谢

Answer 1

在第 5 步试试这个

op.add_column('test1', sa.Column('new_column', sa.String()))