howto ? SQLAlchemyDTO add custom DTOField

[dilkhushvakhabov]

Model:

class OrderModel(UUIDAuditBase):
    __tablename__ = "orders"
    amount: Mapped[int]  # Only amount field as per requirements
    users: Mapped[list["UserModel"]] = relationship(
        secondary=user_order_association,
        back_populates="orders",
        lazy="selectin"
    )
  
DTO:

class OrderCreateDTO(SQLAlchemyDTO[OrderModel]):
    """Data Transfer Object for creating an Order."""
    
    config = SQLAlchemyDTOConfig(
        include={"amount", "user_ids"},
    )
    user_ids: list[UUID] = DTOField(
        mark=Mark.WRITE_ONLY
    )

@post("/", dto=OrderCreateDTO)
async def create_order(self, order_service: OrderService, data: DTOData[OrderModel]) -> OrderModel:
    order = await order_service.create(data)
    return order

{
  "amount": 0,
  "user_ids": ["UUID-1", "UUID-2"]
}

this code is not working :(

[provinzkraut]

This is not a supported feature.

Conceptually, DTOs are not designed to work this way.

Examining your code closely:

data: DTOData[OrderModel] means "I want a DTOData object here, having all the fields of the DTO for OrderModel".

class OrderCreateDTO(SQLAlchemyDTO[OrderModel]):
    config = SQLAlchemyDTOConfig(
        include={"amount", "user_ids"},
    )

and this means "Create a DTO for OrderModel and include its amount and user_ids fields". But OrderModel does not have a user_ids field.

---

The simple answer is, that if you want a field on your model, you'll have to put it on your model. DTOs are intended to transform data from one shape to another; They are not intended to model data.