Python SqlAlchemy - AttributeError：映射器

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一个新会话：

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)

我不知道这个错误来自哪里，我无法真正调试它..有人可以帮助我解决这个问题吗？

谢谢并问候！

查看回溯，您可以看到这些行：

  ...
  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
  ...

这大大缩小了你的问题范围。关系

    user = relationship('model.user.User', back_populates='sessions')

使用 Python 可计算字符串作为argument，其用途在中进一步解释“配置关系”:

与其他类的关系以通常的方式完成，并添加了该类指定的附加功能relationship()可能是一个字符串名称。关联的“类注册表”Base在映射器编译时用于将名称解析为实际的类对象，一旦使用映射器配置，预计就会被定义

如果您还没有导入models.user在尝试实例化模块之前的任何地方Session第一次对象，然后名称解析失败，因为类User尚未创建且不存在于注册表中。换句话说，为了使名称解析有效，所有类都必须已定义，这意味着它们的主体必须已被执行。

如果您确实导入了models.user模块，检查您的其他模型以及它们相关的模型类是否已定义。第一次使用模型会触发映射器编译/配置，因此错误的来源可能是其他型号以及。