Alembic SQLAlchemy 自动生成元数据错误

Question

我正在尝试使用运行 alembic revision --autogenerate -m 'initial setup' 的 alembic 创建迁移，但出现错误：

失败：无法继续使用 --autogenerate 选项；环境脚本 /Users/paul/python/my_project/alembic/env.py 不向上下文提供 MetaData 对象或对象序列。

我无法弄清楚为什么会出现此错误，因为我在 env.py 文件中设置了 target_metadata，并将文件夹添加到路径中。我尝试从我的另一个可以正常工作的项目中复制 alembic 设置，但我仍然在该项目上遇到相同的错误。当我运行 alembic current 时，数据库会毫无问题地创建。

我的 alembic.ini 文件：

# A generic, single database configuration.

[alembic]
# path to migration scripts
script_location = alembic

# template used to generate migration files
# file_template = %%(rev)s_%%(slug)s

# timezone to use when rendering the date
# within the migration file as well as the filename.
# string value is passed to dateutil.tz.gettz()
# leave blank for localtime
# timezone =

# max length of characters to apply to the
# "slug" field
# truncate_slug_length = 40

# set to 'true' to run the environment during
# the 'revision' command, regardless of autogenerate
# revision_environment = false

# set to 'true' to allow .pyc and .pyo files without
# a source .py file to be detected as revisions in the
# versions/ directory
# sourceless = false

# version location specification; this defaults
# to alembic/versions.  When using multiple version
# directories, initial revisions must be specified with --version-path
# version_locations = %(here)s/bar %(here)s/bat alembic/versions

# the output encoding used when revision files
# are written from script.py.mako
# output_encoding = utf-8

sqlalchemy.url = sqlite:///./src/db/data.sqlite


# Logging configuration
[loggers]
keys = root,sqlalchemy,alembic

[handlers]
keys = console

[formatters]
keys = generic

[logger_root]
level = WARN
handlers = console
qualname =

[logger_sqlalchemy]
level = WARN
handlers =
qualname = sqlalchemy.engine

[logger_alembic]
level = INFO
handlers =
qualname = alembic

[handler_console]
class = StreamHandler
args = (sys.stderr,)
level = NOTSET
formatter = generic

[formatter_generic]
format = %(levelname)-5.5s [%(name)s] %(message)s
datefmt = %H:%M:%S

我的 env.py 文件：

import sys

from logging.config import fileConfig
from pathlib import Path

from sqlalchemy import engine_from_config
from sqlalchemy import pool

from alembic import context

folder = Path(__file__).resolve().parents[1]
sys.path.insert(0, str(folder))

import src.data.__all_models
from src.data.modelbase import SqlAlchemyBase

# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = SqlAlchemyBase.metadata

# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.


def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url, target_metadata=target_metadata, literal_binds=True
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection, target_metadata=target_metadata
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

我的 modelbase.py 文件：

import sqlalchemy.ext.declarative as dec


SqlAlchemyBase = dec.declarative_base()

错误消息显示了 env.py 文件的正确路径，因此它似乎正在查找文件但没有看到 target_metadata = SqlAlchemyBase.metadata 行。

Answer 1

问题出在我的编辑器上。我关闭了 env.py 文件，重新打开它，并按预期进行了所有更改。然后我决定看看如果我通过命令+从控制台中的错误消息中单击它来打开文件会发生什么（我正在使用 VSCode），并且当我以这种方式打开它时我的任何更改都没有。我尝试再次从侧面文件资源管理器打开文件，我的更改在文件中，但 alembic 仍然无法运行。我完全关闭了 VSCode 并重新打开它，然后更改在我的文件中并且 alembic 运行没有问题。

我以前从未遇到过这个问题，所以我不知道 VSCode 发生了什么，但无论它重新启动它都解决了问题。

Answer 2

我遇到了同样的错误。我的问题是格式错误的env.py。特别是，我的数据库定义如下：

# alembic.ini

[alembic]
...
databases = db1, db2
...

虽然元数据定义未对齐，例如：

#env.py

target_metadata = {
    "wrong_name_1": model_db1.Base.metadata,  # Key should be "db1"
    "wrong_name_2": model_db2.Base.metadata   # Key should be "db2"
}