FastAPI allows to define query params in Pydantic model. It works perfectly fine as long as we write non-Annotated Code but Annotated code failed to display query param metadata(description, examples) in Swagger UI.

# non-Annotated Code
class QueryParams(BaseModel):
    query_param1: str | None = Field(
        Query(
            None,
            description="Description for query-param-1.",
            example="example-for-query-param-1",
        )
    )
    query_param2: str | None = Field(
        Query(
            None,
            description="Description for query-param-2.",
            example="example-for-query-param-1",
        )
    )



@router.get("/")
async def get_products(query_params: QueryParams = Depends()):
    ...

• Annotated code failed to display query parameters metadata(description, examples) in Swagger UI.

# Annotated Code
class QueryParams(BaseModel):
    query_param1: Annotated[
        str | None,
        Field(
            Query(
                description="Description for query-param-1.",
                example="example-for-query-param-1",
            )
        ),
    ] = None
    query_param2: Annotated[
        str | None,
        Field(
            Query(
                description="Description for query-param-2.",
                example="example-for-query-param-1",
            )
        ),
    ] = None



@router.get("/")
async def get_products(query_params: QueryParams = Depends()):
    ...