Is there a bug in the single body pass parameter?

[ciaoyizhen]

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• I'm @tiangolo or he asked me directly to create an issue here.

Issue Content

server

from fastapi import FastAPI
import uvicorn
from pydantic import BaseModel

app = FastAPI()

class InputParams(BaseModel):
    name:str

@app.post("/")
async def index(params:InputParams):
    return f"hello {params.name}"


uvicorn.run(app)

client

import requests
import json

host = "http://localhost:8000"
uri = "/"
url = host + uri


body = {"name": "aaa"}

response = requests.post(url, json=body)
print(response.status_code)
print(response.json())

It's OK.
server

from fastapi import FastAPI, Body
import uvicorn

app = FastAPI()

@app.post("/")
async def index(name:str=Body(), age:int=Body()):
    return f"hello {name}, {age}"


uvicorn.run(app)

client

import requests
import json

host = "http://localhost:8000"
uri = "/"
url = host + uri


body = {"name": "aaa", "age":18}

response = requests.post(url, json=body)
print(response.status_code)
print(response.json())

OK again.

server

from fastapi import FastAPI, Body
import uvicorn
from pydantic import BaseModel

app = FastAPI()

class InputParams(BaseModel):
    name:str
    age:int

@app.post("/")
async def index(params:InputParams):
    return f"hello {params.name, params.age}, "


uvicorn.run(app)

client

import requests
import json

host = "http://localhost:8000"
uri = "/"
url = host + uri


body = {"name": "aaa", "age":18}

response = requests.post(url, json=body)
print(response.status_code)
print(response.json())

ok. No problem.

But!!!!
server

from fastapi import FastAPI, Body
import uvicorn

app = FastAPI()

@app.post("/")
async def index(name:str=Body()):
    return f"hello {name}"


uvicorn.run(app)

client

import requests
import json

host = "http://localhost:8000"
uri = "/"
url = host + uri


body = {"name": "aaa"}

response = requests.post(url, json=body)
print(response.status_code)
print(response.json())

It's failed. why??? very confuse!!!

How should I call it, or where can I get knowledge about it. will the next version of fastapi be able to support this call?
help me thank you very much!

[ciaoyizhen]

422
{'detail': [{'type': 'string_type', 'loc': ['body'], 'msg': 'Input should be a valid string', 'input': {'name': 'aaa'}}]}

[ciaoyizhen]

import requests
import json

host = "http://localhost:8000"
uri = "/"
url = host + uri

body = {"name": "aaa"}

response = requests.post(url, json="aaa")
print(response.status_code)
print(response.json())

this is correct. but why?

[ciaoyizhen]

In fact, such a modification can be very problematic, as there are inconsistencies in calling the method when there is only one body and multiple bodies

[PhysicallyActive]

If you want to be able to only take one input parameter, you can do the following:

from fastapi import FastAPI, Body
import uvicorn
from typing import Annotated

app = FastAPI()

@app.post("/")
async def index(name: Annotated[str, Body(embed=True)]):
    return f"hello {name}"


uvicorn.run(app)

For a reference to the Body (in particular the embed) documentation:
https://fastapi.tiangolo.com/reference/parameters/?h=body+embed#fastapi.Body

When embed is True, the parameter will be expected in a JSON body as a key instead of being the JSON body itself.
This happens automatically when more than one Body parameter is declared.

[ciaoyizhen]

thank you. It work