Can SQLAlchemy model classes each have a ForeignKey column pointing to each other?

I have two SQLAlchemy classes, each having a foreign key pointing to the other class.

class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True)
    user_name = Column(String, nullable=false)
    company_id = Column(Integer, ForeignKey("companies.id")
    
    company = relationship("Item", back_populates="users")

class Company(Base):
    __tablename__ = "companies"

    id = Column(Integer, primary_key=True)
    name = Column(String)
    modified_by = Column(Integer, ForeignKey("users.id")

    users = relationship("User", back_populates="company")

I get this error

sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship User.company - there are multiple foreign key paths linking the tables.  Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.

I know from searching online that SQLAlchemy cannot determine the join condition between parent and child tables due to multiple foreign key paths linking the tables.

Is this considered bad practice and should I remove one of the foreign keys?

I tried adding the foreign_keys argument in the relationship function, but it didn't help.

Please give a good explanation of how this should be handled.

Thanks

This is a "thing". The docs talk about it here (second case): rows-that-point-to-themselves-mutually-dependent-rows

import sys
from sqlalchemy import (
    create_engine,
    Integer,
    String,
)
from sqlalchemy.schema import (
    Column,
    ForeignKey,
)
from sqlalchemy.sql import select
from sqlalchemy.orm import declarative_base, Session, aliased, relationship, joinedload


Base = declarative_base()


username, password, db = sys.argv[1:4]


engine = create_engine(f"postgresql+psycopg2://{username}:{password}@/{db}", echo=True)


class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True)
    user_name = Column(String, nullable=False)
    company_id = Column(Integer, ForeignKey("companies.id"))
    company = relationship("Company", back_populates="users", primaryjoin="User.company_id == Company.id")
    modified_companies = relationship("Company", back_populates="modified_by", primaryjoin="User.id == Company.modified_by_id", post_update=True)


class Company(Base):
    __tablename__ = "companies"

    id = Column(Integer, primary_key=True)
    name = Column(String)
    # added _id suffix to prevent clash with relationship
    modified_by_id = Column(Integer, ForeignKey("users.id"), nullable=True)
    modified_by = relationship("User", primaryjoin=modified_by_id == User.id, post_update=True)
    users = relationship("User", primaryjoin=id == User.company_id, back_populates="company")

Base.metadata.create_all(engine)

with Session(engine) as session:
    u1 = User(user_name="user1")
    c1 = Company(name="company1", users=[u1], modified_by=u1)
    session.add(c1)
    session.commit()

with Session(engine) as session:
    company = session.execute(select(Company)).scalar()
    assert len(company.users) == 1
    assert company.users[0] == company.modified_by

here are the important logs, you can see post update:

2023-06-07 16:43:55,569 INFO sqlalchemy.engine.Engine BEGIN (implicit)
2023-06-07 16:43:55,571 INFO sqlalchemy.engine.Engine INSERT INTO companies (name, modified_by_id) VALUES (%(name)s, %(modified_by_id)s) RETURNING companies.id
2023-06-07 16:43:55,571 INFO sqlalchemy.engine.Engine [generated in 0.00019s] {'name': 'company1', 'modified_by_id': None}
2023-06-07 16:43:55,574 INFO sqlalchemy.engine.Engine INSERT INTO users (user_name, company_id) VALUES (%(user_name)s, %(company_id)s) RETURNING users.id
2023-06-07 16:43:55,574 INFO sqlalchemy.engine.Engine [generated in 0.00017s] {'user_name': 'user1', 'company_id': 1}
2023-06-07 16:43:55,577 INFO sqlalchemy.engine.Engine UPDATE companies SET modified_by_id=%(modified_by_id)s WHERE companies.id = %(companies_id)s
2023-06-07 16:43:55,577 INFO sqlalchemy.engine.Engine [generated in 0.00018s] {'modified_by_id': 1, 'companies_id': 1}
2023-06-07 16:43:55,579 INFO sqlalchemy.engine.Engine COMMIT