Enhancement: Use Pydantic `model_config` for determining `alias` usage in OpenAPI schema

[sobolevn]

Description

Let's say I have this app:

from litestar import Litestar, post
from litestar.openapi import OpenAPIConfig
from litestar.openapi.plugins import SwaggerRenderPlugin
from pydantic import BaseModel, Field

class Item(BaseModel):
    field_name: str = Field(alias="fieldName")


@post("/")
async def handler(data: Item) -> Item:
    return data

app = Litestar(
    route_handlers=[handler],
    openapi_config=OpenAPIConfig(
        title="Test",
        version="1.0.0",
        render_plugins=[SwaggerRenderPlugin()],
    ),
)

It shows me this API docs:

Everything works as expected.
We get Item as an input schema, then return it.

Now, when I change data: Item to be something else, like data: str, my schema changes in an incompatible way :)

@post("/")
async def handler(data: str) -> Item:
    return Item(fieldName=data)

Now it is:

Notice: camelCase -> snake_case. Which will break existing code for existing users of my API.

Which is kinda expected, because .model_dump() by default produces:

>>> Item(fieldName='abc').model_dump()
{'field_name': 'abc'}

But, setting serialize_by_alias also does not change the produced schema:

In [1]: from pydantic import BaseModel, Field, ConfigDict
   ...: 
   ...: class Item(BaseModel):
   ...:     field_name: str = Field(alias="fieldName")
   ...:     model_config = ConfigDict(serialize_by_alias=True)
   ...: 

In [2]: Item(fieldName='abc').model_dump()
Out[2]: {'fieldName': 'abc'}

So, this looks like a bug to me :)

URL to code causing the issue

No response

MCVE

Steps to reproduce

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2. Click on '....'
3. Scroll down to '....'
4. See error

Screenshots

No response

Logs

Litestar Version

2.17.0

Platform

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

[provinzkraut]

You need to set prefer_alias=True in the PydanticPlugin:

app = Litestar(
    route_handlers=[handler],
    plugins=[PydanticPlugin(prefer_alias=True)],
)

Currently the per-model configuration is not respected. Would make sense to do so, but that would be a feature request, not a bug :)

[sobolevn]

Thanks! Updated 👍