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我ModelBase为我的基于 SQLAlchemy 的应用程序创建了一个类。

为了节省我不得不输入的繁琐工作，id = Column(Integer, primary_key=True)我在我的ModelBase班级中提供了该属性作为默认 ID。

Base = declarative_base()

class ModelBase(AbstractConcreteBase, Base):
    id = Column(Integer, primary_key=True)

    def __init__(self, *args, **kwargs):
        """ constructor """
        # do some nifty magic, keyword cleaning on kwargs, as we might have data 
        # coming from json input 
        super(ModelBase,self).__init__(*args, **kwargs)

    def do_sth_else(self):
         """ some shared fundamental logic, json (de)serialization """

我可能不应该这样做，因为现在所有类都有一个 id 整数字段。事实证明，我想在某些模型上使用复合键，但我仍然希望将模型类的默认值id作为主键。所以我决定写一个mixin类，提供不同的ModelBase类。

Base = declarative_base()

class IDMixin(object):
    id = Column(Integer, primary_key=True)

class AbstractModelBase(object):

    def __init__(self, json_data='', *args, **kwargs):
        """ same constructor """
        super(AbstractModelBase,self).__init__(*args, **kwargs)

    def do_sth_else(self):
         """ same shared fundamental logic """

class ModelBase(AbstractConcreteBase, Base, IDMixin, AbstractModelBase):
    """ new model base class """

class NoIDModelBase(AbstractConcreteBase, Base, AbstractModelBase):
    """ new model base class """

然而，用关键字字典实例化这个类给了我一个痛苦的堆栈跟踪：

$ ./manage.py test # no, not django ;)
# Test 1 of 30
===============
Traceback (most recent call last):
  File "./manage.py", line 40, in <module>
    execute_command(sys.argv)
  File "./manage.py", line 36, in execute_command
    cmd(argv[2:])
  File "./management/test.py", line 362, in handle
    DBtestRunner(verbosity=args.verbosity).run(tests)
  File "./management/test.py", line 172, in run
    setUpDB(t)
  File "./management/test.py", line 134, in setUpDB
    instance = model_class(**d) ### instantiation occurs here ###
  File "<string>", line 2, in __init__
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", line 310, in _new_state_if_none
    state = self._state_constructor(instance, self)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 582, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/orm/instrumentation.py", line 145, in _state_constructor
    self.dispatch.first_init(self, self.class_)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/event.py", line 409, in __call__
    fn(*args, **kw)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2197, in _event_on_first_init
    configure_mappers()
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2123, in configure_mappers
    _call_configured.dispatch.after_configured()
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/event.py", line 372, in __call__
    fn(*args, **kw)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/orm/events.py", line 489, in wrap
    wrapped_fn(*arg, **kw)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/base.py", line 51, in go
    cls.__declare_last__()
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/ext/declarative/api.py", line 347, in __declare_last__
    cls.__mapper__ = m = mapper(cls, pjoin, polymorphic_on=pjoin.c.type)
  File "/path/to/code/refactoring/.env/lib/python2.7/site-packages/sqlalchemy/util/_collections.py", line 172, in __getattr__
    raise AttributeError(key)
AttributeError: type

在这个方法中调用模型类的构造函数：

def setUpDB(test):
    test.db_engine = create_engine('sqlite:///:memory:', convert_unicode=True)
    session_factory.configure(bind=test.db_engine)
    db_session = scoped_session(session_factory)
    ModelBase.metadata.create_all(test.db_engine)

    test.client = Client(app, Response)

    if (hasattr(test, "fixtures")):
        # load fixtures from json
        fixtures = test.fixtures
        if isinstance(fixtures, basestring):
            fixtures = (fixtures, )
        elif isinstance(fixtures, collections.Iterable):
            pass
        else:
            raise Exception(
                "fixtures attribute needs to be string or iterable of strings")

        for fixture in fixtures:
            try:
                with open(fixture, 'r') as f:
                    fixture = json.loads(f.read())

                # apply fixture to database
                for entry in fixture:
                    model = entry["model"]
                    # import the module containing the Model class
                    model_module = importlib.import_module(
                        model[:model.rfind(".")])
                    # get the model class
                    model_class = getattr(
                        model_module, model[model.rfind(".") + 1:])

                    # create an instance of the model class for
                    # each entry in "data"
                    data = entry["data"]
                    for d in data:
                        instance = model_class(**d)
                        instance.save()
            except IOError as e:
                print "Could not load Fixture!\n"
                print e
                sys.exit(1)
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1 回答 1

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您可能有比您从回溯中注意到的更深层次的问题（尽管它可能是相关的）。 Column需要为数据库中的每个实际列调用一次，如果 4 个表有id列，那么您需要创建相同数量的Column对象。

幸运的是，这正是declared_attr. 您还可以使用参数安排declarative_base在所有子类中设置一些通用功能cls。结合两者：

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr


class ModelBase(object):

    def __init__(self, json_data='', *args, **kwargs):
        """ same constructor """
        super(ModelBase,self).__init__(*args, **kwargs)

    def do_sth_else(self):
         """ same shared fundamental logic """


Base = declarative_base(cls=ModelBase)

class IDMixin(object):
    @declared_attr
    def id(cls):
        return Column(Integer, primary_key=True)

class ModelBase(Base, IDMixin):
    """ new model base class """

class NoIDModelBase(Base):
    """ new model base class """
于 2013-07-25T17:07:38.593 回答