烧瓶不安分属性错误："NoneType"对象没有属性"_sa_instance_state"

Question

我当前正在使用Flask、Flask-SQLAlchemy&Flask-Restless为小型私有AngularJS应用程序提供REST路由。到目前为止，我已经能够有效地制定/使用不包括任何关系的路线。

然而，我有一些表必须与其他表有关系，这就是我的问题所在

  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/local/lib/python2.7/dist-packages/flask_restless/views.py", line 145, in decorator
    return func(*args, **kw)
  File "/usr/local/lib/python2.7/dist-packages/mimerender.py", line 227, in wrapper
    result = target(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/flask/views.py", line 84, in view
    return self.dispatch_request(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/flask/views.py", line 149, in dispatch_request
    return meth(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/flask_restless/views.py", line 1263, in post
    self.session.add(instance)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/scoping.py", line 150, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1492, in add
    self._save_or_update_state(state)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1510, in _save_or_update_state
    halt_on=self._contains_state):
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 2457, in cascade_iterator
    visited_states, halt_on))
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/relationships.py", line 1449, in cascade_iterator
    get_all_pending(state, dict_)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/dynamic.py", line 185, in get_all_pending
    c.all_items
AttributeError: 'NoneType' object has no attribute '_sa_instance_state'

我认为这个错误与我的模型有关。以下是我目前的模型定义：

surveyOptions = db.Table('survey_options',
    db.Column('survey_id', db.Integer, db.ForeignKey('survey.id')),
    db.Column('option_id', db.Integer, db.ForeignKey('option.id')),
    db.Column('count', db.Integer)                      
    )
class Survey(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    category = db.Column(db.String(50))
    question = db.Column(db.Text)
    startDate = db.Column(db.DateTime)
    endDate = db.Column(db.DateTime)
    options = db.relationship('Option', secondary=surveyOptions,
        backref=db.backref('surveys', lazy='dynamic'), lazy='dynamic')
def __init__(self, category, question, startDate=None, endDate=None, options=None):
    self.category = category
    self.question = question
    if startDate == None:
        self.startDate = datetime.utcnow()
    if endDate == None:
        self.endDate = datetime.utcnow()
    self.options.append(options)
class Option(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    text = db.Column(db.Text)
    def __init__(self, text):
        self.text = text
...
manager = flask.ext.restless.APIManager(app, flask_sqlalchemy_db=db)
manager.create_api(Survey, methods=['GET','POST','PUT','DELETE'], include_columns=['id','category', 'question', 'startDate','endDate', '_options.id','options.text']);

我真的很感激在隔离这个错误的来源方面提供一些帮助。我不确定下一步该如何解决此错误。

如果需要，我可以根据要求为前端和后端提供更多的代码示例。

Answer 1

这是因为在本节中，您似乎在添加一个列表：

def __init__(self, category, question, startDate=None, endDate=None, options=None):
    self.category = category
    self.question = question
    if startDate == None:
        self.startDate = datetime.utcnow()
    if endDate == None:
        self.endDate = datetime.utcnow()
    self.options.append(options)  # assuming options is a list, this will fail.

这是一个问题的原因很简单。如果我有我的选项列表：

foo = ['one', 'two']

我想再添加几个选项：

bar = ['three', 'four']

如果我foo.append(bar)，我得到：

foo = ['one', 'two', ['three', 'four']]

而你实际上正在寻找foo + bar，它会给你：

foo = ['one', 'two', 'three', 'four']

当你解决了这个问题后，你仍然会遇到第二个更奇怪的问题——如果你在创建Survey对象时没有指定options，那么，按照目前的情况，你的代码将尝试对你的对象使用self.options.append(None)。你需要添加一个检查：

if choices:  # None or [] will evaluate to False
    self.choices += choices

我还注意到，您使用==运算符与None进行比较，实际上应该使用is来进行这些比较，例如if startDate is None:。