(MRE位于问题底部)
在 tortoise-orm 中,我们必须等待反向外键字段,如下所示:
comments = await Post.get(id=id).comments
但是在 fastapi 中,当返回 Post 实例时,pydantic 会提示:
pydantic.error_wrappers.ValidationError: 1 validation error for PPost
response -> comments
value is not a valid list (type=type_error.list)
这是有意义的,因为 comments
属性返回协程。我必须使用这个小技巧来获得 aronud:
post = Post.get(id=id)
return {**post.__dict__, 'comments': await post.comments}
但是,真正的问题是当我有多个关系时:返回用户及其帖子及其评论。在这种情况下,我必须以一种非常丑陋的方式将我的整个模型转换为 dict (这听起来不太好)。
这是要重现的代码(尽量保持简单):
models.py
from tortoise.fields import *
from tortoise.models import Model
from tortoise import Tortoise, run_async
async def init_tortoise():
await Tortoise.init(
db_url='sqlite://db.sqlite3',
modules={'models': ['models']},
)
await Tortoise.generate_schemas()
class User(Model):
name = CharField(80)
class Post(Model):
title = CharField(80)
content = TextField()
owner = ForeignKeyField('models.User', related_name='posts')
class PostComment(Model):
text = CharField(80)
post = ForeignKeyField('models.Post', related_name='comments')
if __name__ == '__main__':
run_async(init_tortoise())
__all__ = [
'User',
'Post',
'PostComment',
'init_tortoise',
]
main.py
import asyncio
from typing import List
from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from models import *
app = FastAPI()
asyncio.create_task(init_tortoise())
# pydantic models are prefixed with P
class PPostComment(BaseModel):
text: str
class PPost(BaseModel):
id: int
title: str
content: str
comments: List[PPostComment]
class Config:
orm_mode = True
class PUser(BaseModel):
id: int
name: str
posts: List[PPost]
class Config:
orm_mode = True
@app.get('/posts/{id}', response_model=PPost)
async def index(id: int):
post = await Post.get_or_none(id=id)
return {**post.__dict__, 'comments': await post.comments}
@app.get('/users/{id}', response_model=PUser)
async def index(id: int):
user = await User.get_or_none(id=id)
return {**user.__dict__, 'posts': await user.posts}
/users/1
错误如下:
pydantic.error_wrappers.ValidationError: 1 validation error for PUser
response -> posts -> 0 -> comments
value is not a valid list (type=type_error.list)
您也可能希望将其放入 init.py 中并运行:
import asyncio
from models import *
async def main():
await init_tortoise()
u = await User.create(name='drdilyor')
p = await Post.create(title='foo', content='lorem ipsum', owner=u)
c = await PostComment.create(text='spam egg', post=p)
asyncio.run(main())
我想要的是让 pydantic 自动等待这些异步字段(这样我就可以返回 Post 实例)。 pydantic 怎么可能做到这一点?
更改/posts/{id}
以返回帖子及其所有者而不带评论实际上在使用这种方式时有效(感谢@papple23j):
return await Post.get_or_none(id=id).prefetch_related('owner')
但不适用于反向外键。另外 select_lated('comments')
也没有帮助,它引发了 AttributeError: can't set attribute
。
最佳答案
对不起,我太笨了。
我想到的一个解决方案是使用tortoise.contrib.pydantic
包:
PPost = pydantic_model_creator(Post)
# used as
return await PPost.from_tortoise_orm(await Post.get_or_none(id=1))
但根据 this question ,在声明模型之前需要初始化Tortoise,否则不会包含Relation。所以我很想替换这一行:
asyncio.create_task(init_tortoise())
...与:
asyncio.get_event_loop().run_until_complete(init_tortoise())
但它出错了事件循环已在运行
并删除了 uvloop 和 installing nest_asyncio helped with that.
我使用的解决方案
根据 documentation :
Fetching foreign keys can be done with both async and sync interfaces.
Async fetch:
events = await tournament.events.all()
Sync usage requires that you call fetch_related before the time, and then you can use common functions.
await tournament.fetch_related('events')
在使用 .fetch_lated)
(或在查询集上使用 prefetch_lated
)后,反向外键将变成一个可迭代对象,可以像列表一样使用。但 pydantic 仍然会提示这不是一个有效的列表,因此需要使用验证器:
class PPost(BaseModel):
comments: List[PPostComment]
@validator('comments', pre=True)
def _iter_to_list(cls, v):
return list(v)
(请注意,据我所知,验证器不能是异步的)
由于我设置了 orm_mode
,我必须使用 .from_orm
方法😅:
return PPost.from_orm(await Post.get_or_none(id=42))
Remember, a few hours of trial and error can save you several minutes of looking at the README.
关于python - 如何在异步属性上进行pydantic等待(tortoise-orm的反向ForeignKey)?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/67154219/