python - Flask ReSTLess 属性错误 : 'NoneType' object has no attribute '_sa_instance_state'

Question

我目前正在使用 Flask、Flask-SQLAlchemy 和 Flask-ReSTLess 为小型私有(private) AngularJS 应用程序提供 REST 路由。到目前为止，我已经能够有效地创建/使用不包含任何关系的路线。

但是，我有一些表必须与其他表有关系，这就是我的问题所在。当向 Flask-ReSTLess 路由进行 POST 时，我收到以下 Flask 错误:

  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。这是我当前的模型定义:

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']);

我非常感谢您提供一些帮助来隔离此错误的根源。我不确定下一步该去哪里解决此错误。

如果需要，我可以根据要求提供更多前端和后端代码示例。

Answer 1

这是因为您似乎在本节中附加了一个列表:

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.

这个问题的原因很简单。如果我有我的选项列表:

foo = ['one', 'two']

我想为其添加更多选项:

bar = ['three', 'four']

如果我foo.append(bar)我得到:

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

而您实际上正在寻找 foo + bar ，它会给您:

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

当您解决该问题时，您仍然会遇到第二个更奇怪的问题 - 如果您在创建 Survey 对象时未指定 options，那么就目前而言，您的代码将尝试将 self.options.append(None) 添加到您的对象。您需要为此添加检查:

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，您实际上应该使用 is 进行这些比较，例如如果 startDate 为 None:。