Adding _init_private_attributes to SQLModel __init__ function.

[alexisgaziello]

Fixing:

Private attributes cannot be used in SQLModel. Attributes initialized with PrivateAttr cannot be found.

Proposed solution:

Add a missing line from Pydantic source code.

Note: the class method from_orm does have this initialization.

Related issues:

#149 mentions this issue

Disclaimer

This is my first-ever contribution to an open-source project. I would appreciate any kind of feedback.

[t1mk1k]

Thanks for the fix! I've used it as a workaround in my project by adding it to the init method of my own model.

I noticed that when I loaded a model from the database the private attributes were not initialized because the init in SQLModel is not called. I had to call it separately on the model before being able to use the private attribute.

Have you tested whether your fix works when loading a model from the database?

[alexisgaziello]

Thanks for the fix! I've used it as a workaround in my project by adding it to the init method of my own model.

I noticed that when I loaded a model from the database the private attributes were not initialized because the init in SQLModel is not called. I had to call it separately on the model before being able to use the private attribute.

Have you tested whether your fix works when loading a model from the database?

Do you mean in an example such as the one below?

test_id = uuid4()


class Hero(SQLModel, table=True):
    id: UUID = Field(default_factory=uuid4, primary_key=True)
    _private_hero_attribute: str = PrivateAttr(default="private hero value")

    metadata = MetaData()


with Session(engine) as session:
    hero_rusty_man = Hero(
        id=test_id,
    )
    session.add(hero_rusty_man)
    session.commit()

with Session(engine) as session:
    statement = select(Hero).where(Hero.id == test_id)
    hero = session.exec(statement).scalars().first()

    assert hero._private_hero_attribute == "private hero value"  # this fails

    hero = Hero.from_orm(hero)
    assert hero._private_hero_attribute == "private hero value"  # this doesn't fail

Indeed, when running SQLAlchemy, the private attributes don't get correctly initialized.
Calling the method from_orm solves the problem for this particular case. Not ideal.

I haven't figured out if there is a way to "automate" this process. Maybe SQLAlchemy is using another init/factory_function?

[github-actions]

📝 Docs preview for commit 844e21c at: https://639ce0b204318b01e2823f64--sqlmodel.netlify.app

[lucasgadams]

Whats the status of this?

[lucas-labs]

Any chance we can get this merged?

[alexisgaziello]

@lucas-labs the reality is that the fix doesn't fully work, as shown in #472 (comment)

[AAraKKe]

Calling the method from_orm solves the problem for this particular case. Not ideal.

This is the way this works in Pydantic; the method is called from init, from_orm, and construct; we need to call it from any place where initialization is required. Could you release this fix? We have the entire infrastructure from a base model from where all objects inherit from a BaseModel to make it much simpler to handle connections. Still, without the ability to use private attributes, this makes it impossible to handle.

I imagine this is the case for many users since a model that represents a database object might need to have more often attributes that do not necessary link to the database itself and are used for internal logic.

[sharenz]

I think I am also running into this issue. I am retrieving an object from the database and want to copy it like described in the fastapi docs for partial updates.

object_from_db = session.exec(select_cmd).one_or_none()

copied_object = object_from_db.model_copy() 

The model_copy results in the following error:
object has no attribute '__pydantic_extra__'. Did you mean: '__pydantic_private__'?

Is there a workaround I can use?

[overgodofchaos]

Maybe it will help someone.

If I need to use an attribute that will not be linked to the database, I use attributes with double double underscores.

class Hero(SQLModel, table=True):
    id: int = Field(primary_key=True)
    name: str = Field(...)
    __private_hero_attribute__: str = "private hero value"

They work, but there is no validation applied to them.

[Seluj78]

Ping, this is still needed !

[YuriiMotov]

@alexisgaziello, thanks for your efforts!

Do you have any plans to continue working on this?

[github-actions]

This pull request has a merge conflict that needs to be resolved.

[github-actions]

As this PR has been waiting for the original user for a while but seems to be inactive, it's now going to be closed. But if there's anyone interested, feel free to create a new PR.