Validations in Annotated like AfterValidator do not work in FastAPI 0.115.10 #13440
Description
Discussed in #13431
Originally posted by amacfie-tc February 28, 2025
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Example Code
from typing import Annotated
from pydantic import AfterValidator
from fastapi import FastAPI
app = FastAPI()
def validator(v):
raise ValueError()
Ints = Annotated[list[int], AfterValidator(validator)]
@app.post("/")
def post(ints: Ints) -> None:
return NoneDescription
If we run the code and send a request to the endpoint, e.g.
echo -n '[2,3,4]' | http POST http://localhost:8000
on version 0.115.9, we get a 422 but on 0.115.10 we get 200. Is this a bug?
Operating System
Linux
Operating System Details
No response
FastAPI Version
0.115.10
Pydantic Version
2.9.2, 2.10.6
Python Version
3.12
Additional Context
No response
@tiangolo writes:
This was introduced here: #13314
I'm currently investigating and a fix will be released shortly.
The problem is only when using Annotated directly in FastAPI parameters, when used inside of Pydantic models the validators work (raise) as expected:
from typing import Annotated
from fastapi import FastAPI
from pydantic import AfterValidator, BaseModel
app = FastAPI()
def validator(v):
raise ValueError()
Ints = Annotated[list[int], AfterValidator(validator)]
class Model(BaseModel):
ints: Ints
@app.post("/")
def post(ints: Model) -> None:
return None