Declared attributes aren't supported

I’m using SQLAlchemy’s declared_attr decorator to add columns and relationships.

However, the decorated columns and relationships are completely ignored.

Here is a very simplified reproducer:

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative.api import declared_attr
from sqlalchemy.orm import relationship
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer


Base = declarative_base()


class Person(Base):
    __tablename__ = 'people'

    id = Column(Integer, primary_key=True)
    

class EmailAddress(Base):
    __tablename__ = 'emails'

    @declared_attr
    def owner_id(self) -> Column:
        return Column(Integer, ForeignKey('people.id'), nullable=False)
    
    @declared_attr
    def owner(self) -> relationship:
        return relationship(Person)


me = Person()
email_address = EmailAddress(owner=me)

This is what mypy says:

$ pipenv run mypy decl_attr.py 
decl_attr.py:30: error: Unexpected column "owner" for model "EmailAddress"

[subhamagr]

Any updates on this feature request?

[aydumoulin]

@wbobeirne thanks for trying it out and your feedback

As a sidenote In editor Pylance type checking sometimes produces errors due to lack of mypy plugin support. Is mypy producing the same errors when ran on this file?

This is an expunged version of the solution I use in our codebase. The following code runs in production and passes mypy and pylance.

from typing import TYPE_CHECKING, cast
from uuid import UUID

from sqlalchemy import Column


if TYPE_CHECKING:
    CStr = Column[str]
    CUUID = Column[UUID]
else:
    CStr = str
    CUUID = UUID

class _TypedBase:
    """typed base for mypy purposed"""

    external_id: CStr
    revision_id: CUUID

class _BaseModel(_TypedBase):
    """
    In order to defined common foreign key we need to declare it in a mixin class
    -> Columns with foreign keys to other columns must be declared as @declared_attr callables on declarative mixin classes.
    """

    @declared_attr
    def external_id(self):
        return Column(String(512), nullable=False)

    @declared_attr
    def revision_id(self):
        return cast(CUUID, Column(UUID, ForeignKey("revisions.id", ondelete="CASCADE"))

class User(Model, _BaseModel):
    """user"""

    __tablename__ = "users"

    email = Column(String, nullable=False)
    first_name = Column(String(254), nullable=False)
    last_name = Column(String(254), nullable=False)
    deleted_at = Column(DateTime, nullable=True)

    def __init__(self):
        self.external_id = "test"

See the hover tooltip