Why doesn't FlaskSQLAlchemyBase inherit from model_class arg

[quentinboudinel]

Is there a reason why FlaskSQLAlchemyBase (dynamically created in SQLALchemy._make_declarative_base) has to be sort of a copy of the class passed to model_class (using its dict and bases) instead of just inherit from it ?

I'm asking the question because I encountered an issue where I could not define init_subclass on the class (Base) I passed to model_class. When calling super() inside of Base, it would raise an error as my models are not subclasses of Base.

from flask_sqlalchemy import SQLAlchemy
from sqlalchemy.orm import DeclarativeBase

class Base(DeclarativeBase):
    def __init_subclass__(cls, **kw):
        super().__init_subclass__(**kw)

db = SQLAlchemy(model_class=Base)

class MyModel(db.Model): ...

>>> TypeError: super(type, obj): obj must be an instance or subtype of type