Query parameters from Depends do not show description in docs

First Check

• I added a very descriptive title to this issue.
• I used the GitHub search to find a similar issue and didn’t find it.
• I searched the FastAPI documentation, with the integrated search.
• I already searched in Google “How to X in FastAPI” and didn’t find any information.
• I already read and followed all the tutorial in the docs and didn’t find an answer.
• I already checked if it is not related to FastAPI but to Pydantic.
• I already checked if it is not related to FastAPI but to Swagger UI.
• I already checked if it is not related to FastAPI but to ReDoc.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from fastapi import Depends, FastAPI, Query
from pydantic import BaseModel, Field

app = FastAPI()


class CommonParams(BaseModel):
    a: int = Field(
        1,
        description="Description does not show up in docs",
    )
    b: int = Query(2, description="Using query changes nothing")


@app.get("/")
async def get_root(
    params: CommonParams = Depends(),
    q: int = Query(5, description="This description shows up"),
):
    return {
        "a": params.a,
        "b": params.b,
        "q": q,
    }

Description

Open browser, go to docs page, look at parameters for default route.

Note that description shows up for q parameter, but not for a or b. The schema for a and b in openapi.json does not have a description, but q does.

I expect the description for the fields to show up.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.75.0

Python Version

3.8.11

Additional Context

No response

[jdratlif]

This is a workaround, and I see that it works with python dataclasses, too, but I still think it should work with pydantic models.

from dataclasses import dataclass

from fastapi import Depends, FastAPI, Query

app = FastAPI()


@dataclass
class CommonParams:
    a: int = Query(1, description="describes A")
    b: int = Query(2, description="Describes B")


@app.get("/")
async def get_root(
    params: CommonParams = Depends(),
    q: int = Query(5, description="This description shows up"),
):
    return {
        "a": params.a,
        "b": params.b,
        "q": q,
    }

[long2ice]

By reading source code I found solution:

class CommonParams(BaseModel):
    a: int = Field(
        Query(...,example=1,description="Description does not show up in docs",
    )
    b: int = Query(
        Query(..., example=2, description="Using query changes nothing")
    ) # this is also ok

The code is here: https://github.com/tiangolo/fastapi/blob/master/fastapi/dependencies/utils.py#L361

Which is not so obvious, but really effective.