SQLAlchemy 'Connection' 对象没有属性 '_Inspector__engine'

Question

我想使用 SQLAlchemy 读取未映射到对象的数据库（需要访问开发时未知的数据库）。其中一项功能是读取不同 table 的列名。因此我写了这个连接器：

MyConnector.py

import sqlalchemy as db

class MyConnector:
    __engine = None

    def __init__(self, db_connection):
        self.__engine = db.create_engine(db_connection)

    def __get_table(self, tbl_name):
        metadata = db.MetaData()
        table = db.Table(tbl_name, metadata)
        inspector = db.inspect(self.__engine)
        inspector.reflect_table(table, None)
        return table

    def get_table_columns(self, tbl_name):
        table = self.__get_table(tbl_name)
        return table.columns.keys()

通过以下单元测试进行测试：

ConnectorTest.py

import unittest
from MyConnector import MyConnector

class MyTestCase(unittest.TestCase):
    db_string = "sqlite:///myTest.db"
    expected_columns_user = ["id", "f_name", "l_name", "note"]
    expected_columns_address = ["id", "street", "number", "postal_code", "additional_information", "fk_user"]

    def test_get_table_columns_user(self):
        connector = MyConnector(self.db_string)
        answer = connector.get_table_columns("user")
        self.assertListEqual(self.expected_columns_user, answer)

    def test_get_table_columns_address(self):
        connector = MyConnector(self.db_string)
        answer = connector.get_table_columns("address")
        self.assertListEqual(self.expected_columns_address, answer)


if __name__ == '__main__':
    unittest.main()

SQLite DB 只包含这两个空 tables:

CREATE TABLE user (
    id INTEGER NOT NULL DEFAULT AUTO_INCREMENT,
    f_name VARCHAR,
    l_name VARCHAR,
    note VARCHAR,
    PRIMARY KEY (
        id
    )
);

CREATE TABLE address (
    id INTEGER NOT NULL DEFAULT AUTO_INCREMENT,
    street VARCHAR NOT NULL,
    number INTEGER,
    postal_code INTEGER NOT NULL,
    additional_information VARCHAR,
    fk_user INTEGER NOT NULL,
    PRIMARY KEY (
        id
    ),
    FOREIGN KEY (
        fk_user
    )
    REFERENCES user(id) ON DELETE CASCADE
);

测试 test_get_table_columns_user 按预期工作。测试 test_get_table_columns_address 引发错误：

Error
Traceback (most recent call last):
  File "ConnectorTest.py", line 17, in test_get_table_columns_address
    answer = connector.get_table_columns("address")
  File "MyConnector.py", line 17, in get_table_columns
    table = self.__get_table(tbl_name)
  File "MyConnector.py", line 13, in __get_table
    inspector.reflect_table(table, None)
  File "venv\lib\site-packages\sqlalchemy\engine\reflection.py", line 802, in reflect_table
    reflection_options,
  File "venv\lib\site-packages\sqlalchemy\engine\reflection.py", line 988, in _reflect_fk
    **reflection_options
  File "<string>", line 2, in __new__
  File "venv\lib\site-packages\sqlalchemy\util\deprecations.py", line 298, in warned
    return fn(*args, **kwargs)
  File "venv\lib\site-packages\sqlalchemy\sql\schema.py", line 601, in __new__
    metadata._remove_table(name, schema)
  File "venv\lib\site-packages\sqlalchemy\util\langhelpers.py", line 72, in __exit__
    with_traceback=exc_tb,
  File "venv\lib\site-packages\sqlalchemy\util\compat.py", line 207, in raise_
    raise exception
  File "venv\lib\site-packages\sqlalchemy\sql\schema.py", line 596, in __new__
    table._init(name, metadata, *args, **kw)
  File "venv\lib\site-packages\sqlalchemy\sql\schema.py", line 676, in _init
    resolve_fks=resolve_fks,
  File "venv\lib\site-packages\sqlalchemy\sql\schema.py", line 705, in _autoload
    with insp._inspection_context() as conn_insp:
  File "AppData\Local\Programs\Python\Python37\lib\contextlib.py", line 112, in __enter__
    return next(self.gen)
  File "venv\lib\site-packages\sqlalchemy\engine\reflection.py", line 217, in _inspection_context
    sub_insp = self._construct(self.__class__._init_connection, conn)
  File "venv\lib\site-packages\sqlalchemy\engine\reflection.py", line 117, in _construct
    init(self, bind)
  File "venv\lib\site-packages\sqlalchemy\engine\reflection.py", line 135, in _init_connection
    self.engine = connection.__engine
AttributeError: 'Connection' object has no attribute '_Inspector__engine'

因为两个测试运行完全相同的代码，除了 table 名称的参数，我对结果很困惑。

使用 Google 我发现了这个 PR：https://github.com/laughingman7743/PyAthena/pull/65/files 似乎与此问题无关（引擎，而不是连接）。

很多关于 Sessions 的帖子（比如 Python SQLAlchemy Query: AttributeError: 'Connection' object has no attribute 'contextual_connect' or https://github.com/sqlalchemy/sqlalchemy/issues/4046）。这应该无关紧要，因为在这种情况下使用 Inspector 似乎甚至不需要调用 engine.connect().

为了排除延迟锁或类似问题，我还将test_get_table_columns_address的参数更改为"user"。这适用于断言，显然不匹配。所以对我来说 table (-name?) 看起来像个问题——这很奇怪。

对 SQLAlchemy 有更多经验和洞察力的人能否指出，where/what 我的代码存在问题？提前致谢！

Python 3.7.4

SQLAlchemy 1.4.20

Answer 1

太糟糕了，我不能给任何人一个更好的答案，我怀疑依赖关系的东西被搞砸了......我想尝试不同版本的 SQLAlchemy 来编写具有上述行为的错误报告。因此，我通过以下命令更改了我的 venv 几次：

pip freeze > uninstall.txt
pip uninstall -r uninstall.txt -y
pip install -r requirements.txt

同时将 requirements.txt 更改为几个不同的 SQLAlchemy 版本。请注意，requirements.txt 始终只包含一个需求（不同版本的 SQLAlchemy）。

看到每一个被测试的版本都按预期运行并在单元测试中从问题中成功，我改回了 1.4.20。现在即使是 1.4.20 版本，单元测试也能成功。

为了避免其他文件的影响，项目始终只包含两个py文件和db。所以我认为我们可以排除项目本身的变化是一个原因。正如@snakecharmerb 指出的那样，我还尝试了 _ 和 __ 的“privates”。测试通过双下划线和单下划线成功。所以我唯一的猜测是，首先是需求出了问题。遗憾的是我不能回去检查第一个 uninstall.txt 因为它被覆盖了很多次。

SQLAlchemy 'Connection' 对象没有属性 '_Inspector__engine'

SQLAlchemy 'Connection' object has no attribute '_Inspector__engine'

python

sqlite

sqlalchemy

python-3.x