"TypeError: cannot pickle 'module' object" exception when using a nested sqlalchemy field

[teodoryantcheff]

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Example Code

Full details including code in the Description below

Description

We are using sqlmodel 0.0.8 with a pre-existing sqlite database that has a column with

Field(sa_column=sa.Column(sam.types.CompressedJSONType))

We are implementing a very simple rest API fetching data from the said database.

This is the SQLModel model (stripped down to demo the issue):

class ZIPCode(SQLModel, table=True):
    __tablename__ = 'simple_zipcode'

    zipcode: str = Field(primary_key=True)
    common_city_list: list = Field(sa_column=sa.Column(sam.types.CompressedJSONType))

Using this for the fastapi part:

@app.get("/zip/{zipcode}", response_model=ZIPCode)  # notice the response_model
async def by_zipcode(*, db: Session = Depends(get_db),
                     zipcode: str = Path(regex=ZIP_RE)):
    zipc = db.get(ZIPCode, zipcode)
    if not zipc:
        raise HTTPException(status_code=404, detail=f'{zipcode} not found')
    return zipc

Just starting results in the following, lengthy exception:

$ uvicorn main:app --host 127.0.0.1 --port 8000 --reload
INFO:     Will watch for changes in these directories: ['/mnt/e/src/sgt-geodata/src']
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [9162] using WatchFiles
Loading settings for: Local
2023-04-05 11:39:16,150 INFO sqlalchemy.engine.Engine BEGIN (implicit)
2023-04-05 11:39:16,150 INFO sqlalchemy.engine.Engine PRAGMA main.table_info("simple_zipcode")
2023-04-05 11:39:16,150 INFO sqlalchemy.engine.Engine [raw sql] ()
2023-04-05 11:39:16,152 INFO sqlalchemy.engine.Engine COMMIT
db created
Process SpawnProcess-1:
Traceback (most recent call last):
  File "/usr/lib/python3.11/multiprocessing/process.py", line 314, in _bootstrap
    self.run()
  File "/usr/lib/python3.11/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/uvicorn/_subprocess.py", line 76, in subprocess_started
    target(sockets=sockets)
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/uvicorn/server.py", line 59, in run
    return asyncio.run(self.serve(sockets=sockets))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/asyncio/runners.py", line 190, in run
    return runner.run(main)
           ^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "uvloop/loop.pyx", line 1517, in uvloop.loop.Loop.run_until_complete
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/uvicorn/server.py", line 66, in serve
    config.load()
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/uvicorn/config.py", line 471, in load
    self.loaded_app = import_from_string(self.app)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/uvicorn/importer.py", line 21, in import_from_string
    module = importlib.import_module(module_str)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 1206, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1178, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1149, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 690, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 940, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/mnt/e/src/sgt-geodata/src/main.py", line 55, in <module>
    @app.get("/zip/{zipcode}", response_model=ZIPCode)
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/fastapi/routing.py", line 661, in decorator
    self.add_api_route(
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/fastapi/routing.py", line 600, in add_api_route
    route = route_class(
            ^^^^^^^^^^^^
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/fastapi/routing.py", line 417, in __init__
    ] = create_cloned_field(self.response_field)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/fastapi/utils.py", line 114, in create_cloned_field
    use_type = create_model(original_type.__name__, __base__=original_type)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "pydantic/main.py", line 1026, in pydantic.main.create_model
  File "/mnt/e/src/sgt-geodata/venv_linux/lib/python3.11/site-packages/sqlmodel/main.py", line 272, in __new__
    new_cls = super().__new__(cls, name, bases, dict_used, **config_kwargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "pydantic/main.py", line 138, in pydantic.main.ModelMetaclass.__new__
  File "pydantic/utils.py", line 693, in pydantic.utils.smart_deepcopy
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
                             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
            ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 211, in _deepcopy_tuple
    y = [deepcopy(a, memo) for a in x]
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 211, in <listcomp>
    y = [deepcopy(a, memo) for a in x]
         ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
                             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
            ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 211, in _deepcopy_tuple
    y = [deepcopy(a, memo) for a in x]
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 211, in <listcomp>
    y = [deepcopy(a, memo) for a in x]
         ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
                             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
            ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
                             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 172, in deepcopy
    y = _reconstruct(x, memo, *rv)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 271, in _reconstruct
    state = deepcopy(state, memo)
            ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 146, in deepcopy
    y = copier(x, memo)
        ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 231, in _deepcopy_dict
    y[deepcopy(key, memo)] = deepcopy(value, memo)
                             ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/copy.py", line 161, in deepcopy
    rv = reductor(4)
         ^^^^^^^^^^^
TypeError: cannot pickle 'module' object

If we remove response_model=ZIPCode from the endpoint definition

@app.get("/zip/{zipcode}"  # no response_model
async def by_zipcode(*, db: Session = Depends(get_db),
                     zipcode: str = Path(regex=ZIP_RE)):
......

OR

@app.get("/zip/{zipcode}", response_model=dict)  # plain dict as response_model
async def by_zipcode(*, db: Session = Depends(get_db),
                     zipcode: str = Path(regex=ZIP_RE)):
......

It's all good, no explosions were observed.

Also, since I prefer to have the response model for documentation purposes, for example, we tried defining a "pure" pydantic model:

class ZIPCodeResponse(BaseModel):  # inheriting from BaseModel
    zipcode: str
    common_city_list: list

and setting this as response_model

@app.get("/zip/{zipcode}", response_model=ZIPCodeResponse)
async def by_zipcode(*, db: Session = Depends(get_db),
                     zipcode: str = Path(regex=ZIP_RE)):
......

Works as expected - no exceptions thrown, data is returned, and all.
But I don't reslly think it should be done like this,

Looked at #540, fastapi/fastapi#5514, pydantic/pydantic#380, https://stackoverflow.com/questions/70567929/how-to-use-json-columns-with-sqlmodel

Using

....
    class Config:
        arbitrary_types_allowed = True 

Makes no difference, still dies with TypeError: cannot pickle 'module' object

Environment:

$ pip freeze
anyio==3.6.2
bcrypt==4.0.1
click==8.1.3
fastapi==0.95.0
greenlet==2.0.2
gunicorn==20.1.0
h11==0.14.0
haversine==2.8.0
httptools==0.5.0
idna==3.4
passlib==1.7.4
prettytable==3.6.0
pydantic==1.10.7
python-dotenv==1.0.0
PyYAML==6.0
sniffio==1.3.0
SQLAlchemy==1.4.41
sqlalchemy-mate==1.4.28.4
sqlalchemy2-stubs==0.0.2a32
sqlmodel==0.0.8
starlette==0.26.1
typing_extensions==4.5.0
uvicorn==0.21.1
uvloop==0.17.0
watchfiles==0.19.0
wcwidth==0.2.6
websockets==11.0

$ python -V
Python 3.11.2

$ uname -a
Linux pc 5.15.90.1-microsoft-standard-WSL2 #1 SMP Fri Jan 27 02:56:13 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Please advice on what we are doing wrong here.

Operating System

Linux, Windows, Other

Operating System Details

No response

SQLModel Version

0.0.8

Python Version

Python 3.11.2

Additional Context

No response

[teodoryantcheff]

Anyone?