如何通过多对多关系链接两个现有记录

Question

我需要将roles添加到staff，以下代码可以工作，但不知何故，它不允许向多个人员添加相同的角色。如果再次分配相同的角色，则会从辅助表中删除以前的分配！为什么会发生这种情况

staff_roles = Table('staff_roles', Base.metadata,
Column('staff_id', Integer, ForeignKey('staff.id')),
Column('role_id', Integer, ForeignKey('roles.id'))
)
class Staff(Base):
__tablename__="staff"
id=             Column(Integer, primary_key=True, index=True)
img=            Column(String)
civil_id=       Column(Integer)
nationality=    Column(String)
disabled=       Column(Boolean, default=False)
created_at=     Column(DateTime)
updated_at=     Column(DateTime)
user_id = Column(Integer, ForeignKey('users.id'), nullable=False)
roles = relationship("Roles", uselist=True, secondary=staff_roles, back_populates="staff", lazy='raise')

class Roles(Base):
__tablename__="roles"
id=             Column(Integer, primary_key=True, index=True)
name=           Column(String)
staff = relationship("Staff", uselist=False, secondary=staff_roles, back_populates="roles", lazy='raise')

def add_role_to_staff(db: Session, user_id:int, role_ids:list):
roles = db.query(tables.Roles).options(joinedload(tables.Roles.staff)).filter(tables.Roles.id.in_(role_ids)).all()
staff = db.query(tables.Staff).options(joinedload(tables.Staff.roles)).filter(tables.Staff.user_id == user_id).first()
if len(roles) == 0 or staff is None:
raise HTTPException(status_code=404, detail="role or staff does not exist")
for role in roles:
staff.roles.append(role)

try:
db.commit()
except IntegrityError as e:
db.rollback()
process_db_error(e)

从日志：

INFO:sqlalchemy.engine.base.Engine:DELETE FROM staff_roles WHERE staff_roles.staff_id = %(staff_id)s AND staff_roles.role_id = %(role_id)s
INFO:sqlalchemy.engine.base.Engine:{'staff_id': 2, 'role_id': 2}
INFO:sqlalchemy.engine.base.Engine:INSERT INTO staff_roles (staff_id, role_id) VALUES (%(staff_id)s, %(role_id)s)
INFO:sqlalchemy.engine.base.Engine:{'staff_id': 1, 'role_id': 2}
INFO:sqlalchemy.engine.base.Engine:COMMIT

为什么它会删除？！

Answer 1

这很有趣，问题出现在staff关系中的Roles表中。uselist应该是True。