Bug: SQLAlchemy models with default=func.now() error with Unexpected default type

[MitPitt]

Description

Columns with default=func.now() will cause SQLAlchemySerializationPlugin to error with ValueError: Unexpected default type.

Workaround is replacing it with server_default=func.now()

URL to code causing the issue

No response

MCVE

from litestar import Litestar, get
from litestar.contrib.sqlalchemy.plugins import SQLAlchemySerializationPlugin
from sqlalchemy import BigInteger, Column, DateTime, String
from sqlalchemy.orm import DeclarativeBase
from sqlalchemy.sql import func


class Base(DeclarativeBase): ...


class User(Base):
    __tablename__ = "users"
    id = Column(BigInteger, primary_key=True)
    username = Column(String)
    first_interaction = Column(DateTime, default=func.now())
    last_interaction = Column(DateTime, default=func.now(), onupdate=func.now())


@get("/{user_id:int}")
async def get_user(user_id: int) -> User:
    user = "pretend this is a User"
    return user


app = Litestar(
    route_handlers=[get_user],
    plugins=[SQLAlchemySerializationPlugin()],
)

Steps to reproduce

No response

Screenshots

No response

Logs

Traceback (most recent call last):
  File "/home/mit/frbot/./asd.py", line 25, in <module>
    app = Litestar(
          ^^^^^^^^^
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/app.py", line 483, in __init__
    self.register(route_handler)
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/app.py", line 667, in register
    route_handler.on_registration(self)
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/handlers/http_handlers/base.py", line 560, in on_registration
    super().on_registration(app)
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/handlers/base.py", line 544, in on_registration
    self.resolve_return_dto()
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/handlers/base.py", line 504, in resolve_return_dto
    return_dto.create_for_field_definition(
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/dto/base_dto.py", line 183, in create_for_field_definition
    backend_context[key] = backend_cls(  # type: ignore[literal-required]
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/dto/_codegen_backend.py", line 72, in __init__
    super().__init__(
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/dto/_backend.py", line 108, in __init__
    self.parsed_field_definitions = self.parse_model(
                                    ^^^^^^^^^^^^^^^^^
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/litestar/dto/_backend.py", line 140, in parse_model
    for field_definition in self.dto_factory.generate_field_definitions(model_type):
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/advanced_alchemy/extensions/litestar/dto.py", line 280, in generate_field_definitions
    yield from cls.handle_orm_descriptor(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/functools.py", line 946, in _method
    return method.__get__(obj, cls)(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/advanced_alchemy/extensions/litestar/dto.py", line 116, in _
    default, default_factory = _detect_defaults(elem)
                               ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/mit/frbot/.venv/lib/python3.11/site-packages/advanced_alchemy/extensions/litestar/dto.py", line 311, in _detect_defaults
    raise ValueError(msg)
ValueError: Unexpected default type

Litestar Version

sqlalchemy = { extras = ["asyncio"], version = "^2.0.29" }
litestar = {extras = ["sqlalchemy", "standard"], version = "^2.8.2"}

Platform

• Linux
• Mac
• Windows
• Other (Please specify in the description above)

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[sion908]

@MitPitt
Hi!!
I also encountered the same error.
And this seems to be an expected error.
As a concept like a responsibility branching point, it seems better not to let the db generate values ​​as much as possible, so use lambda: datetime.now(timezone.utc) instead of func.nou(). However, in this case, I think it can be said that it is good.

like this
And it's in hereadvanced-alchemy

class AuditColumns:
    """Created/Updated At Fields Mixin."""

    created_at: Mapped[datetime] = mapped_column(
        DateTimeUTC(timezone=True),
        default=lambda: datetime.now(timezone.utc),
    )
    """Date/time of instance creation."""
    updated_at: Mapped[datetime] = mapped_column(
        DateTimeUTC(timezone=True),
        default=lambda: datetime.now(timezone.utc),
    )
    """Date/time of instance last update."""

you can import from here

from litestar.plugins.sqlalchemy import AuditColumns

[MitPitt]

@sion908 I am introducing litestar to a project which already had sqlalchemy in it. I would like to keep new litestar code separated from older sqlalchemy stuff. Meaning I don't want to import AuditColumns from litestar. In case I wanted to remove litestar from the project in the future, this would create problems.

But I will try using lambda: datetime.now(), thanks.

[sion908]

I hope it was helpful