Bug: internal error when deleting servers with forward rules

[LeiShi1313]

backend_1   | Sending clean.clean_runner task
backend_1   | INFO:     192.168.176.6:50466 - "DELETE /api/v1/servers/15 HTTP/1.0" 200 OK
backend_1   | INFO:     192.168.176.6:50474 - "GET /api/v2/servers?page=0&size=20 HTTP/1.0" 200 OK
backend_1   | INFO:     192.168.176.6:50498 - "GET /api/v2/servers/29/detailed HTTP/1.0" 200 OK
backend_1   | Sending clean.clean_runner task
backend_1   | INFO:     192.168.176.6:50520 - "DELETE /api/v1/servers/29 HTTP/1.0" 500 Internal Server Error
backend_1   | /usr/local/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py:1359: SAWarning: DELETE statement on table 'server_user' expected to delete 3 row(s); 0 were matched.  Please set confirm_deleted_rows=False within the mapper configuration to prevent this warning.
backend_1   |   util.warn(
backend_1   | /usr/local/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py:1359: SAWarning: DELETE statement on table 'port_user' expected to delete 3 row(s); 0 were matched.  Please set confirm_deleted_rows=False within the mapper configuration to prevent this warning.
backend_1   |   util.warn(
backend_1   | ERROR:    Exception in ASGI application
backend_1   | Traceback (most recent call last):
backend_1   |   File "/usr/local/lib/python3.8/site-packages/uvicorn/protocols/http/h11_impl.py", line 389, in run_asgi
backend_1   |     result = await app(self.scope, self.receive, self.send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
backend_1   |     return await self.app(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/fastapi/applications.py", line 199, in __call__
backend_1   |     await super().__call__(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/applications.py", line 111, in __call__
backend_1   |     await self.middleware_stack(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/errors.py", line 181, in __call__
backend_1   |     raise exc from None
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/errors.py", line 159, in __call__
backend_1   |     await self.app(scope, receive, _send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/base.py", line 25, in __call__
backend_1   |     response = await self.dispatch_func(request, self.call_next)
backend_1   |   File "/app/app/main.py", line 73, in db_session_middleware
backend_1   |     response = await call_next(request)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/base.py", line 45, in call_next
backend_1   |     task.result()
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/base.py", line 38, in coro
backend_1   |     await self.app(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/base.py", line 25, in __call__
backend_1   |     response = await self.dispatch_func(request, self.call_next)
backend_1   |   File "/app/app/main.py", line 65, in sentry_exception
backend_1   |     raise e
backend_1   |   File "/app/app/main.py", line 57, in sentry_exception
backend_1   |     response = await call_next(request)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/base.py", line 45, in call_next
backend_1   |     task.result()
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/base.py", line 38, in coro
backend_1   |     await self.app(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/cors.py", line 86, in __call__
backend_1   |     await self.simple_response(scope, receive, send, request_headers=headers)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/middleware/cors.py", line 142, in simple_response
backend_1   |     await self.app(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/exceptions.py", line 82, in __call__
backend_1   |     raise exc from None
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/exceptions.py", line 71, in __call__
backend_1   |     await self.app(scope, receive, sender)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/routing.py", line 566, in __call__
backend_1   |     await route.handle(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/routing.py", line 227, in handle
backend_1   |     await self.app(scope, receive, send)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/starlette/routing.py", line 41, in app
backend_1   |     response = await func(request)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 209, in app
backend_1   |     response_data = await serialize_response(
backend_1   |   File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 116, in serialize_response
backend_1   |     value, errors_ = field.validate(response_content, {}, loc=("response",))
backend_1   |   File "pydantic/fields.py", line 723, in pydantic.fields.ModelField.validate
backend_1   |     v, errors = self._validate_singleton(v, values, loc, cls)
backend_1   |   File "pydantic/fields.py", line 906, in pydantic.fields.ModelField._validate_singleton
backend_1   |     return self._apply_validators(v, values, loc, cls, self.validators)
backend_1   |   File "pydantic/fields.py", line 913, in pydantic.fields.ModelField._apply_validators
backend_1   |     v = validator(cls, v, values, self, self.model_config)
backend_1   |   File "pydantic/class_validators.py", line 310, in pydantic.class_validators._generic_validator_basic.lambda12
backend_1   |     return lambda cls, v, values, field, config: validator(v)
backend_1   |   File "pydantic/main.py", line 737, in pydantic.main.BaseModel.validate
backend_1   |     return cls.from_orm(value)
backend_1   |   File "pydantic/main.py", line 629, in pydantic.main.BaseModel.from_orm
backend_1   |     values, fields_set, validation_error = validate_model(cls, obj)
backend_1   |   File "pydantic/main.py", line 1040, in pydantic.main.validate_model
backend_1   |     v_, errors_ = field.validate(value, values, loc=field.alias, cls=cls_)
backend_1   |   File "pydantic/fields.py", line 734, in pydantic.fields.ModelField.validate
backend_1   |     v, errors = self._validate_sequence_like(v, values, loc, cls)
backend_1   |   File "pydantic/fields.py", line 767, in pydantic.fields.ModelField._validate_sequence_like
backend_1   |     r, ee = self._validate_singleton(v_, values, v_loc, cls)
backend_1   |   File "pydantic/fields.py", line 899, in pydantic.fields.ModelField._validate_singleton
backend_1   |     value, error = field.validate(v, values, loc=loc, cls=cls)
backend_1   |   File "pydantic/fields.py", line 723, in pydantic.fields.ModelField.validate
backend_1   |     v, errors = self._validate_singleton(v, values, loc, cls)
backend_1   |   File "pydantic/fields.py", line 906, in pydantic.fields.ModelField._validate_singleton
backend_1   |     return self._apply_validators(v, values, loc, cls, self.validators)
backend_1   |   File "pydantic/fields.py", line 913, in pydantic.fields.ModelField._apply_validators
backend_1   |     v = validator(cls, v, values, self, self.model_config)
backend_1   |   File "pydantic/class_validators.py", line 310, in pydantic.class_validators._generic_validator_basic.lambda12
backend_1   |     return lambda cls, v, values, field, config: validator(v)
backend_1   |   File "pydantic/main.py", line 737, in pydantic.main.BaseModel.validate
backend_1   |     return cls.from_orm(value)
backend_1   |   File "pydantic/main.py", line 629, in pydantic.main.BaseModel.from_orm
backend_1   |     values, fields_set, validation_error = validate_model(cls, obj)
backend_1   |   File "pydantic/main.py", line 1019, in pydantic.main.validate_model
backend_1   |     value = input_data.get(field.alias, _missing)
backend_1   |   File "pydantic/utils.py", line 418, in pydantic.utils.GetterDict.get
backend_1   |     return getattr(self._obj, key, default)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/attributes.py", line 294, in __get__
backend_1   |     return self.impl.get(instance_state(instance), dict_)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/attributes.py", line 730, in get
backend_1   |     value = self.callable_(state, passive)
backend_1   |   File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/strategies.py", line 717, in _load_for_state
backend_1   |     raise orm_exc.DetachedInstanceError(
backend_1   | sqlalchemy.orm.exc.DetachedInstanceError: Parent instance <ServerUser at 0x7f933e44a0a0> is not bound to a Session; lazy load operation of attribute 'user' cannot proceed (Background on this error at: http://sqlalche.me/e/13/bhk3)