[BUG]: Unable to serialize unknown type: <class 'beanie.odm.fields.BackLink'>

[advayumare]

Unable to return response model containing BackLink
Getting pydantic serialization error when tying to return model containing BackLink

I have following code

from typing import List
from fastapi import status
from beanie import Document, BackLink, Link, WriteRules
from pydantic import Field

class House(Document):
    name: str
    owner: Link["Person"]

class Person(Document):
    name: str
    house: BackLink[House] = Field(original_field="owner")

@app.post(
    "/house",
    response_model=House,
    status_code=status.HTTP_201_CREATED,
)
async def create_house(
    house: House = Body(...)
):
    person = Person(name="Batman", house=house)
    house.person = person
    await house.save(link_rule=WriteRules.WRITE)
    if house:
        await house.sync()
        return house
    

Expected behavior
After calling post api with following request body

    {
        "name": "Bat Cave"
    }

the response should have been

    {
        "id": "1",
        "name": "Bat Cave",
        "owner": {
            "name": "Batman",
            "house": "1"
        }
    }

instead it gives me following error while serializing owner object

Unable to serialize unknown type: <class 'beanie.odm.fields.BackLink'>

[travka47]

Somebody please help :_)

[07pepa]

@advayumare have you tried this? since your example will only work for pydantic v1

class Person(Document):
    name: str
    house: BackLink[House] = Field(json_schema_extra={"original_field": "owner"})

[travka47]

@07pepa
In my example there is pydantic 2.7

class Feature(Document, FeatureSchema):
    id: PydanticObjectId = Field(default_factory=PydanticObjectId, alias='_id', serialization_alias='id')
    bugreports: Optional[List[BackLink[Bugreport]]] = Field(default=None,
                                                            json_schema_extra={"original_field": "feature"})

    class Settings:
        collection = "features"
        max_nesting_depths_per_field = {
            "bugreports": 1
        }


class FeatureWithoutGeometry(Feature):
    type: SkipJsonSchema[Optional[str]] = Field(default=None, exclude=True)
    geometry: SkipJsonSchema[Optional[Geometry]] = Field(default=None, exclude=True)


class Bugreport(Document, BugreportSchema):
    id: PydanticObjectId = Field(default_factory=PydanticObjectId, alias='_id', serialization_alias='id')
    feature: Link["Feature"]

    class Settings:
        collection = 'bugreports'
        max_nesting_depths_per_field = {
            "feature": 2
        }


features = await Feature.find(fetch_links=False).project(FeatureWithoutGeometry).to_list()

Error appears when fetch_links is False