如何在 FastAPI 响应模式中使用箭头类型？

Question

我想在FastAPI响应中使用Arrow类型，因为我已经在SQLAlchemy模型中使用它（感谢sqlalchemy_utils ）。

我准备了一个带有最小 FastAPI 应用程序的小型独立示例。 我希望这个应用程序从数据库中返回product1数据。

不幸的是，下面的代码给出了异常：

Exception has occurred: FastAPIError
Invalid args for response field! Hint: check that <class 'arrow.arrow.Arrow'> is a valid pydantic field type

import sqlalchemy
import uvicorn
from arrow import Arrow
from fastapi import FastAPI
from pydantic import BaseModel
from sqlalchemy import Column, Integer, Text, func
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy_utils import ArrowType

app = FastAPI()

engine = sqlalchemy.create_engine('sqlite:///db.db')
Base = declarative_base()

class Product(Base):
    __tablename__ = "product"
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(Text, nullable=True)
    created_at = Column(ArrowType(timezone=True), nullable=False, server_default=func.now())

Base.metadata.create_all(engine)


Session = sessionmaker(bind=engine)
session = Session()

product1 = Product(name="ice cream")
product2 = Product(name="donut")
product3 = Product(name="apple pie")

session.add_all([product1, product2, product3])
session.commit()


class ProductResponse(BaseModel):
    id: int
    name: str
    created_at: Arrow

    class Config:
        orm_mode = True
        arbitrary_types_allowed = True


@app.get('/', response_model=ProductResponse)
async def return_product():

    product = session.query(Product).filter(Product.id == 1).first()

    return product

if __name__ == "__main__":
    uvicorn.run(app, host="localhost", port=8000)

要求.txt：

sqlalchemy==1.4.23
sqlalchemy_utils==0.37.8
arrow==1.1.1
fastapi==0.68.1
uvicorn==0.15.0

那些 FastAPI 问题中已经讨论了这个错误：

1. https://github.com/tiangolo/fastapi/issues/1186
2. https://github.com/tiangolo/fastapi/issues/2382

---

一种可能的解决方法是添加此代码（ source ）：

from pydantic import BaseConfig
BaseConfig.arbitrary_types_allowed = True

将它放在@app.get('/'...之上就足够了，但它甚至可以放在app = FastAPI()之前

此解决方案的问题是 GET 端点的输出将是：

// 20210826001330
// http://localhost:8000/

{
  "id": 1,
  "name": "ice cream",
  "created_at": {
    "_datetime": "2021-08-25T21:38:01+00:00"
  }
}

而不是想要的：

// 20210826001330
// http://localhost:8000/

{
  "id": 1,
  "name": "ice cream",
  "created_at": "2021-08-25T21:38:01+00:00"
}

Answer 1

添加一个带有@validator装饰器的自定义函数，该函数返回对象的所需_datetime ：

class ProductResponse(BaseModel):
    id: int
    name: str
    created_at: Arrow

    class Config:
        orm_mode = True
        arbitrary_types_allowed = True

    @validator("created_at")
    def format_datetime(cls, value):
        return value._datetime

在本地测试，似乎工作：

$ curl -s localhost:8000 | jq
{
  "id": 1,
  "name": "ice cream",
  "created_at": "2021-12-02T08:25:10+00:00"
}

Answer 2

解决方案是monkeypatch pydantic 的ENCODERS_BY_TYPE以便它知道如何转换 Arrow 对象以便它可以被 json 格式接受：

from arrow import Arrow
from pydantic.json import ENCODERS_BY_TYPE
ENCODERS_BY_TYPE |= {Arrow: str}

设置BaseConfig.arbitrary_types_allowed = True也是必要的。

结果：

// 20220514022717
// http://localhost:8000/

{
  "id": 1,
  "name": "ice cream",
  "created_at": "2022-05-14T00:20:11+00:00"
}

完整代码：

import sqlalchemy
import uvicorn
from arrow import Arrow
from fastapi import FastAPI
from pydantic import BaseModel
from sqlalchemy import Column, Integer, Text, func
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy_utils import ArrowType

from pydantic.json import ENCODERS_BY_TYPE
ENCODERS_BY_TYPE |= {Arrow: str}

from pydantic import BaseConfig
BaseConfig.arbitrary_types_allowed = True

app = FastAPI()

engine = sqlalchemy.create_engine('sqlite:///db.db')
Base = declarative_base()

class Product(Base):
    __tablename__ = "product"
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(Text, nullable=True)
    created_at = Column(ArrowType(timezone=True), nullable=False, server_default=func.now())

Base.metadata.create_all(engine)


Session = sessionmaker(bind=engine)
session = Session()

product1 = Product(name="ice cream")
product2 = Product(name="donut")
product3 = Product(name="apple pie")

session.add_all([product1, product2, product3])
session.commit()


class ProductResponse(BaseModel):
    id: int
    name: str
    created_at: Arrow

    class Config:
        orm_mode = True
        arbitrary_types_allowed = True


@app.get('/', response_model=ProductResponse)
async def return_product():

    product = session.query(Product).filter(Product.id == 1).first()

    return product

if __name__ == "__main__":
    uvicorn.run(app, host="localhost", port=8000)

Answer 3

这是一个代码示例，您不需要class Config并且可以通过使用验证器创建自己的子类来处理任何类型：

from psycopg2.extras import DateTimeTZRange as DateTimeTZRangeBase
from sqlalchemy.dialects.postgresql import TSTZRANGE
from sqlmodel import (
    Column,
    Field,
    Identity,
    SQLModel,
)

from pydantic.json import ENCODERS_BY_TYPE

ENCODERS_BY_TYPE |= {DateTimeTZRangeBase: str}


class DateTimeTZRange(DateTimeTZRangeBase):
    @classmethod
    def __get_validators__(cls):
        yield cls.validate

    @classmethod
    def validate(cls, v):
        if isinstance(v, str):
            lower = v.split(", ")[0][1:].strip().strip()
            upper = v.split(", ")[1][:-1].strip().strip()
            bounds = v[:1] + v[-1:]
            return DateTimeTZRange(lower, upper, bounds)
        elif isinstance(v, DateTimeTZRangeBase):
            return v
        raise TypeError("Type must be string or DateTimeTZRange")

    @classmethod
    def __modify_schema__(cls, field_schema):
        field_schema.update(type="string", example="[2022,01,01, 2022,02,02)")


class EventBase(SQLModel):
    __tablename__ = "event"
    timestamp_range: DateTimeTZRange = Field(
        sa_column=Column(
            TSTZRANGE(),
            nullable=False,
        ),
    )


class Event(EventBase, table=True):
    id: int | None = Field(
        default=None,
        sa_column_args=(Identity(always=True),),
        primary_key=True,
        nullable=False,
    )

链接到 Github 问题： https ://github.com/tiangolo/sqlmodel/issues/235#issuecomment-1162063590