SqlModel日期时间字段在执行时抛出错误

Question

我在python3.8中使用SQLModel

当我添加日期时间字段created_at: datetime = Field(default_factory=utcnow(), nullable=False)时

我得到了这个错误

File "./app/main.py", line 16, in <module>
    class Post(SQLModel, table=True):
  File "/Users/markwardell/PycharmProjects/pythonProject/venv/lib/python3.8/site-packages/sqlmodel/main.py", line 277, in __new__
    new_cls = super().__new__(cls, name, bases, dict_used, **config_kwargs)
  File "pydantic/main.py", line 204, in pydantic.main.ModelMetaclass.__new__
  File "pydantic/fields.py", line 488, in pydantic.fields.ModelField.infer
  File "pydantic/fields.py", line 419, in pydantic.fields.ModelField.__init__
  File "pydantic/fields.py", line 539, in pydantic.fields.ModelField.prepare
  File "pydantic/fields.py", line 801, in pydantic.fields.ModelField.populate_validators
  File "pydantic/validators.py", line 718, in find_validators
RuntimeError: error checking inheritance of <module 'datetime' from '/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/datetime.py'> (type: module)

如果我不添加created_at，表将按预期在PostgresSql中创建。码

import datetime
from typing import Optional
import utcnow as utcnow
from fastapi import FastAPI
from sqlalchemy import TIMESTAMP, text
from sqlmodel import Field, Session, SQLModel, create_engine, select
from app.database import SQLALCHEMY_DATABASE_URL

class Hero(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)


class Post(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True, nullable=False)
    title: str = Field(nullable=False)
    content: str = Field(nullable=False)
    published: bool = Field(default=True, nullable=False)
    created_at: datetime = Field(default_factory=utcnow(), nullable=False)

engine = create_engine(SQLALCHEMY_DATABASE_URL)


def create_db_and_tables():
    SQLModel.metadata.create_all(engine)


app = FastAPI()


@app.on_event("startup")
def on_startup():
    create_db_and_tables()

Answer 1

这一点在一条评论中作了解释，但只是作为对其他人的回答：

您必须像这样导入日期时间

from datetime import datetime

我们在这个上下文中需要的datetime实际上是一个模块中的一个类，也称为datetime。

Answer 2

另外，请注意，您的代码应该是

created_at: datetime.datetime = Field(default_factory=datetime.utcnow, nullable=False)

如果没有在实例化中调用utcnow，那么这样做将给出在实例化时所参考的每个入口日期时间。因此，default_factory应该是函数，而不是值。