Question

我在同一模块中有两个名为models的模型。它们是1-1关系，并且已根据SQLAlchemy docs进行配置。

Vehicle.py

from models.AssetSetting import AssetSetting

class Vehicle(Base):
     __tablename__ = 'vehicles'

     vehicle_id = Column(Integer, primary_key=True)
     ...
     settings = relationship('AssetSetting', backref=backref('asset_settings'))

AssetSetting.py

from models.Vehicle import Vehicle

class AssetSetting(Base):
     __tablename__ = 'asset_settings'

     asset_alert_setting_id = Column(Integer, primary_key=True, autoincrement=True)
     ...

     vehicle = relationship('vehicles', foreign_keys=Column(ForeignKey('vehicles.vehicle_id')))

如果我使用字符串关系构建（即ForeignKey('vehicles.vehicle_id')），我会收到错误：

sqlalchemy.exc.InvalidRequestError: 
When initializing mapper Mapper|AssetSetting|asset_settings, expression 'vehicles' failed to locate a name ("name 'vehicles' is not defined"). 
If this is a class name, consider adding this relationship() to the <class 'models.AssetSetting.AssetSetting'> class after both dependent classes have been defined.

如果我使用类映射，我会得到经典的循环导入错误：

Traceback (most recent call last):
File "tracking_data_runner.py", line 7, in <module>
from models.Tracker import Tracker
File "/.../models/Tracker.py", line 5, in <module>
from models.Vehicle import Vehicle
File "/.../models/Vehicle.py", line 13, in <module>
from models.Tracker import Tracker
ImportError: cannot import name 'Tracker'

我相信我可以通过将文件放在同一个包中来解决这个问题，但我更愿意将它们分开。想法？

Answer 1

我发现我的问题有两个问题：

我在我的关系中不恰当地引用了relationship('Vehicle'。它应该是relationship('vehicles'而不是foreign_keys=Column(ForeignKey('vehicles.vehicle_id'))
显然在关系中声明FK是不合适的，就像我在 AssetSettings.py （class Vehicle(Base, IDiagnostable, IUsage, ITrackable): __tablename__ = 'vehicles' vehicle_id = Column(Integer, primary_key=True)_id = Column(Integer) settings = relationship('AssetSetting', backref=backref('asset_settings'))）中所做的那样。我必须申报FK，然后将其传递给关系。

我的配置现在看起来像这样：

<强> Vehicle.py

class AssetSetting(Base):
    __tablename__ = 'asset_settings'

    asset_alert_setting_id = Column(Integer, primary_key=True, autoincrement=True)
    vehicle_id = Column(ForeignKey('vehicles.vehicle_id'))

    vehicle = relationship('Vehicle', foreign_keys=vehicle_id)

<强> AssetSetting.py

docker daemon -H 0.0.0.0:2376

Answer 2

为避免循环导入错误，您应该使用字符串关系构建，但您的两个模型都必须使用相同的Base - 相同的{{ 1}}实例。实例化declarative_base一次，并在初始化Base和Vehicle时使用它。

或者，您可以显式映射表名和类，以帮助映射器关联您的模型：

AssetSetting

Answer 3

您的__tablename__引用了vehicles，但您的外键引用了vehicle.vehicle_id

SQLAlchemy模型循环导入

3 个答案: