Nullable relationships require Optional

[amacfie]

Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

Sqlacodegen version

master (66a88dc)

SQLAlchemy version

2.0.19

RDBMS vendor

PostgreSQL

What happened?

Using --generator declarative I get

from typing import List, Optional

from sqlalchemy import ForeignKeyConstraint, Integer, PrimaryKeyConstraint
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column, relationship

class Base(DeclarativeBase):
    pass


class Refers(Base):
    __tablename__ = 'refers'
    __table_args__ = (
        ForeignKeyConstraint(['parent_id'], ['refers.id'], name='refers_parent_id_fkey'),
        PrimaryKeyConstraint('id', name='refers_pkey')
    )

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    parent_id: Mapped[Optional[int]] = mapped_column(Integer)

    parent: Mapped['Refers'] = relationship('Refers', remote_side=[id], back_populates='parent_reverse')
    parent_reverse: Mapped[List['Refers']] = relationship('Refers', remote_side=[parent_id], back_populates='parent')

I believe the type of parent should be Mapped[Optional['Refers']]. SQLAlchemy docs reference.

Database schema for reproducing the bug

CREATE TABLE refers (
    id        SERIAL  PRIMARY KEY,
    parent_id INTEGER,
    FOREIGN KEY (parent_id) REFERENCES refers(id)
);