how to push computed_field into response_model in FastAPI route?

[chapov]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the SQLModel documentation, with the integrated search.
• I already searched in Google "How to X in SQLModel" 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 SQLModel but to Pydantic.
• I already checked if it is not related to SQLModel but to SQLAlchemy.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from fastapi import APIRouter
from pydantic import computed_field, PrivateAttr, BaseModel
from sqlalchemy import table
from sqlmodel import SQLModel, Field, Relationship
from typing import Optional

class Driver(SQLModel, table=True):
    id: Optional[int] = Field(primary_key=True)

class TMBase(SQLModel):
    _y: int = PrivateAttr(default=0)

    @computed_field
    @property
    def y(self) -> int:
        return self._y

    @y.setter
    def y(self, value):
        self._y = value

class TM(TMBase, table=True):
    id: Optional[int] = Field(primary_key=True)
    driver_id: int | None = Field( foreign_key="driver.id")
    driver: "Driver" = Relationship(sa_relationship_kwargs={"lazy": "joined"})

test_router = APIRouter()

class TMResponse(TMBase):
    id: int
    driver: Driver | None = None


class TMResponses(BaseModel):
    items: list[TMResponse]

@test_router.get(
    '/computed-field',
    response_model=TMResponses,
)
async def computed_field():
    tm = TM()
    tm.id = 10000
    tm.y = 20000
    tm.driver = Driver(id=123)

    return {
        "items": [tm],
    }

Description

When I open the /computed_field link, I expect to see the following response:

{
  "items": [
    {
      "id": 10000,
      "driver": {
        "id": 123
      },
      "y": 20000
    }
  ]
}

But instead of what I expected, I see this:

{
  "items": [
    {
      "id": 10000,
      "driver": {
        "id": 123
      },
      "y": 0
    }
  ]
}

Field "y" = 0

If I remove response_model=TMResponses from the route, I get the following response:

{
  "items": [
    {
      "id": 10000,
      "y": 20000
    }
  ]
}

Field "driver" disappears!

How to make it right response_model?

Operating System

Linux

Operating System Details

No response

SQLModel Version

0.0.22

Python Version

Python 3.12.5

Additional Context

pydantic version: 2.9.1
FastAPI version 0.114.0

[chapov]

@computed_field is not needed.
It works without computed_field.
And I don't understand how it works :)