无法在使用夹具的 Pytest function 内实例化 Python 数据类（冻结）

Question

我正在关注 Harry Percival 和 Bob Gregory 在 Python 中的架构模式。

在第三 (3) 章左右，他们介绍了测试 SQLAlchemy 的 ORM。

一个需要session夹具的新测试，由于cannot assign to field '_sa_instance_state'而AttributeError, FrozenInstanceError

可能需要注意的是，其他测试在创建OrderLine实例时不会失败，但如果我只是将session包含到测试参数中，它们就会失败。

无论如何，我会直接进入代码。

conftest.py

@pytest.fixture
def local_db():
    engine = create_engine('sqlite:///:memory:')
    metadata.create_all(engine)
    return engine


@pytest.fixture
def session(local_db):
    start_mappers()
    yield sessionmaker(bind=local_db)()
    clear_mappers()

model.py

@dataclass(frozen=True)
class OrderLine:
    id: str
    sku: str
    quantity: int

test_orm.py

def test_orderline_mapper_can_load_lines(session):
    session.execute(
        'INSERT INTO order_lines (order_id, sku, quantity) VALUES '
        '("order1", "RED-CHAIR", 12),'
        '("order1", "RED-TABLE", 13),'
        '("order2", "BLUE-LIPSTICK", 14)'
    )
    expected = [
        model.OrderLine("order1", "RED-CHAIR", 12),
        model.OrderLine("order1", "RED-TABLE", 13),
        model.OrderLine("order2", "BLUE-LIPSTICK", 14),
    ]
    assert session.query(model.OrderLine).all() == expected

pipenv run pytest test_orm.py的控制台错误

============================= test session starts =============================
platform linux -- Python 3.7.6, pytest-5.4.1, py-1.8.1, pluggy-0.13.1
rootdir: /home/[redacted]/Documents/architecture-patterns-python
collected 1 item                                                              

test_orm.py F                                                           [100%]

================================== FAILURES ===================================
____________________ test_orderline_mapper_can_load_lines _____________________

session = <sqlalchemy.orm.session.Session object at 0x7fd919ac5bd0>

    def test_orderline_mapper_can_load_lines(session):
        session.execute(
            'INSERT INTO order_lines (order_id, sku, quantity) VALUES '
            '("order1", "RED-CHAIR", 12),'
            '("order1", "RED-TABLE", 13),'
            '("order2", "BLUE-LIPSTICK", 14)'
        )
        expected = [
>           model.OrderLine("order1", "RED-CHAIR", 12),
            model.OrderLine("order1", "RED-TABLE", 13),
            model.OrderLine("order2", "BLUE-LIPSTICK", 14),
        ]

test_orm.py:13: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
<string>:2: in __init__
    ???
../../.local/share/virtualenvs/architecture-patterns-python-Qi2y0bev/lib64/python3.7/site-packages/sqlalchemy/orm/instrumentation.py:377: in _new_state_if_none
    self._state_setter(instance, state)
<string>:1: in set
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <[AttributeError("'OrderLine' object has no attribute '_sa_instance_state'") raised in repr()] OrderLine object at 0x7fd919a8cf50>
name = '_sa_instance_state'
value = <sqlalchemy.orm.state.InstanceState object at 0x7fd9198f7490>

>   ???
E   dataclasses.FrozenInstanceError: cannot assign to field '_sa_instance_state'

<string>:4: FrozenInstanceError
=========================== short test summary info ===========================
FAILED test_orm.py::test_orderline_mapper_can_load_lines - dataclasses.Froze...
============================== 1 failed in 0.06s ==============================

附加问题

我理解上面的逻辑以及这些文件在做什么，但如果我缺乏基本的理解，请纠正我。

1. conftest.py (used for all pytest config) is setting up a session fixture, which basically sets up a temporary database in memory - using start and clear mappers to ensure that the orm model definitions are binding to the db isntance.
   
2. model.py只是一个用于表示原子OrderLine object 的数据类。
   
3. test_orm.py class 用于 pytest 以提供session夹具，以便显式setup, execute, teardown数据库以运行测试。

https 提供的问题解决方法：//github.com/cosmicpython/code/issues/17

Answer 1

我正在关注 Harry Percival 和 Bob Gregory 在 Python 中的架构模式。

在第三 (3) 章左右，他们介绍了测试 SQLAlchemy 的 ORM。

一个需要session夹具的新测试，由于cannot assign to field '_sa_instance_state'而AttributeError, FrozenInstanceError

可能需要注意的是，其他测试在创建OrderLine实例时不会失败，但如果我只是将session包含到测试参数中，它们就会失败。

无论如何，我会直接进入代码。

conftest.py

@pytest.fixture
def local_db():
    engine = create_engine('sqlite:///:memory:')
    metadata.create_all(engine)
    return engine


@pytest.fixture
def session(local_db):
    start_mappers()
    yield sessionmaker(bind=local_db)()
    clear_mappers()

model.py

@dataclass(frozen=True)
class OrderLine:
    id: str
    sku: str
    quantity: int

test_orm.py

def test_orderline_mapper_can_load_lines(session):
    session.execute(
        'INSERT INTO order_lines (order_id, sku, quantity) VALUES '
        '("order1", "RED-CHAIR", 12),'
        '("order1", "RED-TABLE", 13),'
        '("order2", "BLUE-LIPSTICK", 14)'
    )
    expected = [
        model.OrderLine("order1", "RED-CHAIR", 12),
        model.OrderLine("order1", "RED-TABLE", 13),
        model.OrderLine("order2", "BLUE-LIPSTICK", 14),
    ]
    assert session.query(model.OrderLine).all() == expected

pipenv run pytest test_orm.py的控制台错误

============================= test session starts =============================
platform linux -- Python 3.7.6, pytest-5.4.1, py-1.8.1, pluggy-0.13.1
rootdir: /home/[redacted]/Documents/architecture-patterns-python
collected 1 item                                                              

test_orm.py F                                                           [100%]

================================== FAILURES ===================================
____________________ test_orderline_mapper_can_load_lines _____________________

session = <sqlalchemy.orm.session.Session object at 0x7fd919ac5bd0>

    def test_orderline_mapper_can_load_lines(session):
        session.execute(
            'INSERT INTO order_lines (order_id, sku, quantity) VALUES '
            '("order1", "RED-CHAIR", 12),'
            '("order1", "RED-TABLE", 13),'
            '("order2", "BLUE-LIPSTICK", 14)'
        )
        expected = [
>           model.OrderLine("order1", "RED-CHAIR", 12),
            model.OrderLine("order1", "RED-TABLE", 13),
            model.OrderLine("order2", "BLUE-LIPSTICK", 14),
        ]

test_orm.py:13: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
<string>:2: in __init__
    ???
../../.local/share/virtualenvs/architecture-patterns-python-Qi2y0bev/lib64/python3.7/site-packages/sqlalchemy/orm/instrumentation.py:377: in _new_state_if_none
    self._state_setter(instance, state)
<string>:1: in set
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <[AttributeError("'OrderLine' object has no attribute '_sa_instance_state'") raised in repr()] OrderLine object at 0x7fd919a8cf50>
name = '_sa_instance_state'
value = <sqlalchemy.orm.state.InstanceState object at 0x7fd9198f7490>

>   ???
E   dataclasses.FrozenInstanceError: cannot assign to field '_sa_instance_state'

<string>:4: FrozenInstanceError
=========================== short test summary info ===========================
FAILED test_orm.py::test_orderline_mapper_can_load_lines - dataclasses.Froze...
============================== 1 failed in 0.06s ==============================

附加问题

我理解上面的逻辑以及这些文件在做什么，但如果我缺乏基本的理解，请纠正我。
1. conftest.py (used for all pytest config) is setting up a session fixture, which basically sets up a temporary database in memory - using start and clear mappers to ensure that the orm model definitions are binding to the db isntance.
2. model.py只是一个用于表示原子OrderLine object 的数据类。
3. test_orm.py class for pytest 提供session夹具，为了setup, execute, teardown一个运行测试的数据库。

Answer 2

从版本 1.14.16 开始，

def dispose(self, class_):` 

必须改为

def unregister(self, class_, manager):` 
````
https://github.com/sqlalchemy/sqlalchemy/compare/rel_1_4_15...rel_1_4_16#diff-fc3d434dae3b60f8b2b448ee1e24165ffa71e75fbb2aeef1b4651e678a095be7R223