FastAPI中SQLAlchemy AttributeError：'function'对象无'scalars'属性

错误现象 #

通过SwaggerUI发送GET请求/api/messages/时触发500内部服务器错误，核心报错信息：

AttributeError: 'function' object has no attribute 'scalars'

错误堆栈 #

RuntimeWarning: Enable tracemalloc to get the object allocation traceback
INFO:     ::1:55262 - "GET /api/messages/ HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/uvicorn/protocols/http/httptools_impl.py", line 426, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 84, in __call__
    return await self.app(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/fastapi/applications.py", line 1115, in __call__
    await super().__call__(scope, receive, send)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/applications.py", line 122, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/fastapi/middleware/asyncexitstack.py", line 20, in __call__
    raise e
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/fastapi/middleware/asyncexitstack.py", line 17, in __call__
    await self.app(scope, receive, send)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/routing.py", line 718, in __call__
    await route.handle(scope, receive, send)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/starlette/routing.py", line 66, in app
    response = await func(request)
               ^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 274, in app
    raw_response = await run_endpoint_function(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/.venv/lib/python3.12/site-packages/fastapi/routing.py", line 191, in run_endpoint_function
    return await dependant.call(**values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/messenger/routers/api/messages/messages.py", line 44, in list_messages
    return await controller.list(filters=filters)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/messenger/controllers/base.py", line 37, in list
    return await self.repository.list(filters=filters)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/Pavel/Desktop/Projects/Messenger2/messenger/repositories/base.py", line 40, in list
    res = await self.session.scalars(query)
                ^^^^^^^^^^^^^^^^^^^^
AttributeError: 'function' object has no attribute 'scalars'

相关代码文件 #

messenger/routers/api/messages/messages.py #

from fastapi import APIRouter, Depends
from fastapi_filter import FilterDepends
from typing import List

from messenger.controllers import MessageController
from messenger.factories import ControllerFactory
from messenger.filters import MessageFilter
from messenger.schemas import MessagesResponseSchema,


router = APIRouter()


@router.get("/")
async def list_messages(
    controller: MessageController = Depends(ControllerFactory().get_message_controller),
    filters: MessageFilter = FilterDepends(MessageFilter),
) -> List[MessagesResponseSchema]:
    return await controller.list(filters=filters)

messenger/factories/controllers.py #

from fastapi import Depends
from sqlalchemy.ext.asyncio import AsyncSession

from messenger.database import get_session
from messenger.controllers import MessageController
from messenger.models import Message
from messenger.repositories import MessagesRepo


class ControllerFactory:
    def get_message_controller(self, db_session: AsyncSession = Depends(get_session)):
        return MessageController(
            repository=MessagesRepo(
                db_session=get_session,
                model=Message,
            )
        )

messenger/database/session.py #

from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession

from messenger.settings import settings
from messenger.models import Base


engine = create_async_engine(
    settings.get_db_url(),
    echo=True,
)


async def get_session() -> AsyncSession:
    session = async_sessionmaker(
        bind=engine
    )
    async with session() as db_session:
        try:
            yield db_session
        finally:
            await db_session.close()

messenger/controllers/messages.py #

from .base import BaseController

from messenger.models import Message
from messenger.repositories import MessagesRepo


class MessageController(BaseController[Message]):
    def __init__(self, repository: MessagesRepo):
        super().__init__(model=Message, repository=repository)

messenger/controllers/base.py #

from fastapi_filter.contrib.sqlalchemy import Filter
from sqlalchemy.sql import func
from typing import Type, TypeVar, Generic, List, Any

from messenger.models import Base
from messenger.repositories import BaseRepo


ModelType = TypeVar("ModelType", bound=Base)


class BaseController(Generic[ModelType]):
    def __init__(
        self,
        repository: BaseRepo,
        model: Type[ModelType]
    ):
        self.model = model
        self.repository = repository


    async def list(
        self,
        filters: Filter,
    ) -> List[ModelType]:
        return await self.repository.list(filters=filters)

messenger/repositories/messages.py #

from sqlalchemy.ext.asyncio import AsyncSession

from messenger.models import Message
from .base import BaseRepo


class MessagesRepo(BaseRepo[Message]):
    def __init__(self, db_session: AsyncSession, model: Message):
        super().__init__(db_session=db_session, model=model)

messenger/repositories/base.py #

from fastapi_filter.contrib.sqlalchemy import Filter
from sqlalchemy.sql.expression import select
from sqlalchemy.ext.asyncio import AsyncSession
from typing import Type, TypeVar, Generic, List

from messenger.models import Base
from messenger.database import get_session


ModelType = TypeVar("ModelType", bound=Base)


class BaseRepo(Generic[ModelType]):
    def __init__(
        self,
        db_session: AsyncSession,
        model: Type[ModelType],
    ):
        self.session = db_session
        self.model = model


    async def list(
        self,
        filters: Filter,
    ) -> List[ModelType]:
        query = filters.filter(select(self.model))
        res = await self.session.scalars(query)
        return res.all()

排查情况 #

查看self.session的所有方法，确认没有scalars方法，方法列表如下：

['__aenter__', '__aexit__', '__await__', '__class__', '__class_getitem__', '__delattr__', '__dir__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_assign_proxied', '_raise_for_not_started', '_regenerate_proxy_for_target', '_retrieve_proxy_for_target', '_sync_transaction', '_target_gced', 'commit', 'rollback', 'start']

已尝试操作 #

重新安装所有依赖，问题仍未解决，希望得到该错误的解决方案。

内容的提问来源于stack exchange，提问作者Pavel