无效的 Pydantic 字段类型 POST 参数 (FastApi) - Python 3.8

Question

我正在尝试使用 FastApi + SqlAlchemy 并且遇到了参数问题。这是我的 Post 参数导致的错误。我做错了什么？

错误信息

fastapi.exceptions.FastAPIError: Invalid args for response field! Hint: check that <class 'app.models.Post'> is a valid pydantic field type

代码

from fastapi import FastAPI, Response, HTTPException
from fastapi.params import Body, Depends

from sqlalchemy.orm import Session
from starlette import status

from . import models
from .database import engine, get_db
from .models import Post

models.Base.metadata.create_all(bind=engine)
app = FastAPI()


@app.get("/posts")
def get_posts(db: Session = Depends(get_db)):
    posts = db.query(models.Post).all()
    return {"data": posts}


@app.post("/posts", status_code = status.HTTP_201_CREATED)
def create_posts(post: Post, db: Session = Depends(get_db)):
    new_post = models.Post(title=post.title, content=post.content, published=post.published)
    # db.add(new_post)
    # db.commit()
    # db.refresh(new_post)
    return {"data": new_post}

帖子类型

from sqlalchemy import Column, Integer, String, Boolean, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.sql.expression import text
from sqlalchemy.sql.sqltypes import TIMESTAMP

from .database import Base


class Post(Base):
    __tablename__ = "postsalchemy"

    id = Column(Integer, primary_key=True, nullable=False)
    title = Column(String, nullable=False)
    content = Column(String, nullable=False)
    published = Column(Boolean, server_default='TRUE', nullable=False)
    created_at = Column(TIMESTAMP(timezone=True),
                        nullable=False, server_default=text('now()'))

Answer 1

FastAPI 使用 Pydantic 库来验证 HTTP 请求和 HTTP 响应正文。 （顺便说一句Pydantic 是一个库，它将为您提供针对给定模式的数据结构验证） 为此，您必须创建一个与您的 sqlalchemy Post 类相对应的 Pydantic Model 类。

请阅读文档here 以了解有关响应模型的更多信息。

仅供参考，这是如何处理您的示例：

from fastapi import FastAPI, Response, HTTPException
from fastapi.params import Body, Depends

from sqlalchemy.orm import Session
from starlette import status

from . import models
from .database import engine, get_db
from .models import Post
from pydantic import BaseModel
from datetime import datetime
from typing import Dict, List

# Define your pydantic response model 
class PostResponse(BaseModel):
    id: int
    title: str
    content: str
    published: bool
    created_at: datetime

models.Base.metadata.create_all(bind=engine)
app = FastAPI()

# Set PostResponse as a response model in the route decorator
@app.get("/posts", response_model=Dict[str, List[PostResponse]])
def get_posts(db: Session = Depends(get_db)):
    posts = db.query(models.Post).all()
    return {"data": posts}


@app.post("/posts", status_code = status.HTTP_201_CREATED, response_model=Dict[str, PostResponse])
def create_posts(post: Post, db: Session = Depends(get_db)):
    new_post = models.Post(title=post.title, content=post.content, published=post.published)
    # db.add(new_post)
    # db.commit()
    # db.refresh(new_post)
    return {"data": new_post}

额外：您可能还对 SQLModel 库感兴趣，它来自 FastAPI 的同一作者，是 SQL Alchemy 和 Pydantic 库的组合，基本上可以让您避免重复（并且只声明一次模型）