Description

We recently upgraded all of our Starlite-based services to v2, in the process of which we turned up this rather puzzling issue. Specifically, it appears that Pydantic validators are not run for input parameters to handler methods. This is rather unintuitive for us and caused some headaches in regards to data parsing/validating/munging, as exemplified in the MCVE below.

What we expected with a handler like this:

async def mwe_bad(data: MyType) -> dict:

would be that the type would be instantiated from the incoming request body and the validators would run to do potential extra checks and/or manipulate the data slightly.

This seemingly does not happen, instead it seems to be the case that the class is filled with data but bypasses its own validators. Not sure how that can occur, but it's what we're observing. See the MVCE for a detailed reproduction. This same issue also occurs with Pydantic v1 by the way, both versions of Pydantic behave the same in this case.

Let me know if you need any additional information and I'll be happy to oblige.

URL to code causing the issue

No response

MCVE

"""
Run with:
uvicorn main:app --reload

Works:
curl --location 'http://localhost:8000/good' --header 'Content-Type: application/json' --data '{"picture": "test"}'

Doesn't work:
curl --location 'http://localhost:8000/bad' --header 'Content-Type: application/json' --data '{"picture": "test"}'
"""

from dataclasses import field

from litestar import Litestar, post
from pydantic import field_validator
from pydantic.dataclasses import dataclass


@dataclass
class MyType:
    picture: list[str] = field(default_factory=list)

    @field_validator("picture", mode="before")
    @classmethod
    def single_picture_validator(cls, v):
        if isinstance(v, str):
            return [v]
        return v


@post("/good")
async def mwe_good(data: dict) -> dict:
    data = MyType(**data)
    return data


@post("/bad")
async def mwe_bad(data: MyType) -> dict:
    return data


app = Litestar([mwe_good, mwe_bad], debug=True)

Steps to reproduce

1. Test the working endpoint: `curl --location 'http://localhost:8000/good' --header 'Content-Type: application/json' --data '{"picture": "test"}'`
2. Test the broken endpoint: `curl --location 'http://localhost:8000/bad' --header 'Content-Type: application/json' --data '{"picture": "test"}'`
3. Observe that Step 2 fails with a validation error that does not occur in Step 1, even though the same type is used.

Screenshots

No response

Logs

No response

Litestar Version

2.2.1

Platform

• Linux
• Mac
• Windows
• Other (Please specify in the description above)