Typing: of_type method not properly generic.

[WAKayser]

Ensure stubs packages are not installed

• No sqlalchemy stub packages is installed (both sqlalchemy-stubs and sqlalchemy2-stubs are not compatible with v2)

Verify if the api is typed

• The api is not in a module listed in #6810 so it should pass type checking

Describe the typing issue

of_type() method for QueryableAttribute is not properly made generic. This causes the type to not be set correctly and the result is not completely determined. This is only a minor nuisance as the correct type is not needed for any other checking.

To Reproduce

# pyright: strict
from typing import reveal_type

from sqlalchemy import create_engine, ForeignKey
from sqlalchemy.orm import (
    scoped_session,
    sessionmaker,
    DeclarativeBase,
    MappedAsDataclass,
    mapped_column,
    Mapped,
    relationship,
)

engine = create_engine("sqlite://")
db_session = scoped_session(sessionmaker(engine))


class Base(MappedAsDataclass, DeclarativeBase):
    pass


class Employee(Base):
    __tablename__ = "employee"
    id: Mapped[int] = mapped_column(primary_key=True)
    team_id: Mapped[int] = mapped_column(ForeignKey("team.id"))
    team: Mapped["Team"] = relationship(
        lazy="noload", init=False, back_populates="employees"
    )

    __mapper_args__ = {
        "polymorphic_on": "type",
        "polymorphic_identity": "employee",
    }


class Team(Base):
    __tablename__ = "team"
    id: Mapped[int] = mapped_column(primary_key=True)
    team_name: Mapped[str]
    employees: Mapped[list[Employee]] = relationship(
        "Employee", lazy="noload", init=False
    )


class Engineer(Employee):
    engineer_info: Mapped[str | None] = mapped_column(nullable=True, default=None)

    __mapper_args__ = {
        "polymorphic_identity": "engineer",
        "polymorphic_load": "inline",
    }


engineer_load = Team.employees.of_type(Engineer)
reveal_type(Team.employees.of_type(Engineer))

Error

MYPY

of_type_test.py:55: error: Need type annotation for "engineer_load" [var-annotated]
of_type_test.py:56: note: Revealed type is "sqlalchemy.orm.attributes.QueryableAttribute[]"

Pyright

.\of_type_test.py:55:1 - error: Type of "engineer_load" is partially unknown
  Type of "engineer_load" is "QueryableAttribute[Unknown]" (reportUnknownVariableType)
.\of_type_test.py:56:13 - information: Type of "Team.employees.of_type(Engineer)" is "QueryableAttribute[Unknown]"

Versions

• OS: Windows 11
• Python: 3.11 and 3.12
• SQLAlchemy: 2.0.30
• Type checker: mypy 1.10.0 and pyright 1.362

Additional context

Changing signature of the of_type method seems to fix it.

from:
def of_type(self, entity: _EntityType[Any]) -> QueryableAttribute[_T]:
to
def of_type(self, entity: _EntityType[_T]) -> QueryableAttribute[_T]:

Mypy:
of_type_test.py:56: note: Revealed type is "sqlalchemy.orm.attributes.QueryableAttribute[of_type_test.Engineer]"
Pyright:
\of_type_test.py:56:13 - information: Type of "Team.employees.of_type(Engineer)" is "QueryableAttribute[Engineer]"

[CaselIT]

Hi,

Thanks for reporting. Could you create a PR?
The tests could go in test/typing/orm/relationship.