基于我的模型：
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.orm import relationship
Base = declarative_base()
class Session(Base):
__tablename__ = 'sessions'
id = Column(Integer, primary_key=True)
token = Column(String(200))
user_id = Column(Integer, ForeignKey('app_users.id'))
user = relationship('model.user.User', back_populates='sessions')
我想通过以下方式实例化新会话：
session = Session(token='test-token-123')
但我得到：
AttributeError: mapper
完整的堆栈跟踪：
Traceback (most recent call last):
File "/home/ubuntu/.local/lib/python3.5/site-packages/falcon/api.py", line 227, in __call__
responder(req, resp, **params)
File "./app_user/register.py", line 13, in on_post
session = Session(token='test-token-123')
File "<string>", line 2, in __init__
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/instrumentation.py", line 347, in _new_state_if_none
state = self._state_constructor(instance, self)
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py", line 764, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/instrumentation.py", line 177, in _state_constructor
self.dispatch.first_init(self, self.class_)
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/event/attr.py", line 256, in __call__
fn(*args, **kw)
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py", line 2976, in _event_on_first_init
configure_mappers()
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py", line 2872, in configure_mappers
mapper._post_configure_properties()
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py", line 1765, in _post_configure_properties
prop.init()
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/interfaces.py", line 184, in init
self.do_init()
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1653, in do_init
self._process_dependent_arguments()
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1710, in _process_dependent_arguments
self.target = self.mapper.mapped_table
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py", line 850, in __getattr__
return self._fallback_getattr(key)
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py", line 828, in _fallback_getattr
raise AttributeError(key)
我不知道这个错误是从哪里来的，我无法真正调试它..有人可以帮助我解决这个问题吗？
谢谢和问候！
查看回溯，您可以看到以下行：
...
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1653, in do_init
self._process_dependent_arguments()
File "/home/ubuntu/.local/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1710, in _process_dependent_arguments
self.target = self.mapper.mapped_table
...
这大大缩小了您的问题范围。关系
user = relationship('model.user.User', back_populates='sessions')
使用 Python 可评估字符串作为参数，其用法在 "配置关系" 中进一步说明：
与其他类的关系以通常的方式完成，并具有附加功能，即指定
relationship()的类可以是字符串名称。与Base关联的"类注册表"在映射器编译时使用，以将名称解析为实际的类对象，该对象应在使用映射器配置后定义
如果在首次尝试实例化Session对象之前尚未将models.user模块导入任何位置，则名称解析将失败，因为类User尚未创建且注册表中不存在。换句话说，要使名称解析起作用，必须已定义所有类，这意味着它们的主体必须已执行。
如果您确实导入了models.user模块，请检查您的其他模型及其相关的模型类是否已定义。首次使用模型会触发映射器编译/配置，因此错误的根源也可能是其他模型。