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我正在尝试创建一个系统，其中Person是一个WorkGroup的一部分，并且每个WorkGroup包含许多Person。Person还包含先前匹配的Person的列表。以下是我到目前为止所拥有的，我能够成功地将测试名称加载到其中。但是，当我在findPartner方法中尝试将一个新的WorkGroup分配给Person 的 workGroup字段时，如下所示：

self.workGroup = WorkGroup(self, newPartner)

我收到错误消息：

AttributeError: 'list' object has no attribute '_sa_instance_state'

这让我很困惑。（我在列表之后包含了更完整的堆栈跟踪）。希望有人能指出错误（我只使用 SQLAlchemy 大约 24 小时，所以我怀疑这是基本的）。

def sanitize(first, last):
    def san(nm):
        return " ".join([part.strip().capitalize().replace(",", "") 
                         for part in nm.split()])
    return san(first) + " " + san(last)


class Person(db.Model):
    __tablename__ = 'person'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(80), unique=True)
    workGroup = db.relationship("WorkGroup", uselist=False)
    prevPairings_id = db.Column(db.Integer, db.ForeignKey('person.id'))
    prevPairings = db.relationship('Person')

    def __init__(self, first, last):
        self.name = sanitize(first, last)
        self.workGroup = None
        self.prevPairings = []

    def __repr__(self):
        return self.name

    def findPartner(self, amongPeople):
        if self.workGroup:
            return # You already have a group
        candidates = [p for p in amongPeople if p is not self and 
                      p not in self.prevPairings and not p.workGroup]
        assert candidates
        newPartner = candidates[0] # Just choose the first available
        self.prevPairings.append(newPartner)
        newPartner.prevPairings.append(self)
        self.workGroup = WorkGroup(self, newPartner)
        newPartner.workGroup = self.workGroup

    def show(self):
        print "<Person %r %r %r %r>" % (self.id, self.name, self.prevPairings, self.workGroup)


class WorkGroup(db.Model):
    __tablename__ = 'workgroup'
    id = db.Column(db.Integer, primary_key=True)
    members_id = db.Column(db.Integer, db.ForeignKey('person.id'))
    members = db.relationship('Person')

    def __init__(self, *partners):
        self.members = list(partners)

    def include(self, newMember):
        assert isinstance(newMember, Person)
        self.members.append(newMember)

    def group(self):
        return set(self.members)

    def __nonzero__(self):
        return bool(self.members)

    def __iter__(self):
        return iter(self.members)

    def clear(self):
        self.members = []

    def __str__(self): return str(self.members)
    def __repr__(self): return self.__str__()


############################################################

def generateNewPairings():
    all = Person.query.all()
    if max([len(p.prevPairings) for p in all]) > len(all) - 2:
        print "All Pairings Exhausted"
        for p in all:
            p.prevPairings = []
    for p in all:
        p.workGroup = None

    def pairUp(everyone):
        if len(everyone) % 2: # Odd number
            oddOne = random.choice(everyone)
            everyone.remove(oddOne)
            pairUp(everyone) # Recurse with even number
            random.choice(everyone).workGroup.include(oddOne)
            return
        for p in everyone: # Even number
            p.findPartner(everyone)

    pairUp(all)
    for p in all: print p.show()

这是完整的堆栈跟踪：

File "C:\Python27\lib\site-packages\flask\app.py", line 1701, in __call__
return self.wsgi_app(environ, start_response)
File "C:\Python27\lib\site-packages\flask\app.py", line 1689, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "C:\Python27\lib\site-packages\flask\app.py", line 1687, in wsgi_app
response = self.full_dispatch_request()
File "C:\Python27\lib\site-packages\flask\app.py", line 1360, in full_dispatch_request
rv = self.handle_user_exception(e)
File "C:\Python27\lib\site-packages\flask\app.py", line 1358, in full_dispatch_request
rv = self.dispatch_request()
File "C:\Python27\lib\site-packages\flask\app.py", line 1344, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "C:\Users\Bruce Eckel\Dropbox\AtomicScala\_AtomicScalaSeminarLocalServer\AtomicScalaSeminarSQLAlchemy.py", line 242, in generate_pairs
generateNewPairings()
File "C:\Users\Bruce Eckel\Dropbox\AtomicScala\_AtomicScalaSeminarLocalServer\AtomicScalaSeminarSQLAlchemy.py", line 120, in generateNewPairings
pairUp(all)
File "C:\Users\Bruce Eckel\Dropbox\AtomicScala\_AtomicScalaSeminarLocalServer\AtomicScalaSeminarSQLAlchemy.py", line 114, in pairUp
pairUp(everyone) # Recurse with even number
File "C:\Users\Bruce Eckel\Dropbox\AtomicScala\_AtomicScalaSeminarLocalServer\AtomicScalaSeminarSQLAlchemy.py", line 118, in pairUp
p.findPartner(everyone)
File "C:\Users\Bruce Eckel\Dropbox\AtomicScala\_AtomicScalaSeminarLocalServer\AtomicScalaSeminarSQLAlchemy.py", line 63, in findPartner
self.workGroup = WorkGroup(self, newPartner)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py", line 238, in __set__
instance_dict(instance), value, None)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py", line 736, in set
value = self.fire_replace_event(state, dict_, value, old, initiator)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py", line 756, in fire_replace_event
value = fn(state, value, previous, initiator or self)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 89, in set_
sess._save_or_update_state(newvalue_state)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\session.py", line 1389, in _save_or_update_state
halt_on=self._contains_state):
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1928, in cascade_iterator
parent_dict, visited_states, halt_on))
File "C:\Python27\lib\site-packages\sqlalchemy\orm\properties.py", line 929, in cascade_iterator
get_all_pending(state, dict_)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\attributes.py", line 693, in get_all_pending
ret = [(instance_state(current), current)]
AttributeError: 'list' object has no attribute '_sa_instance_state'
4

1 回答 1

2

我认为问题在于您db.relationship()在两者中都使用Person和WorkGroup类。将其设置在其中一个中，并使用backref关键字参数来定义另一侧的关系。

另一个问题是您将外键放在错误的类中。由于您希望和（一个工作组中的许多人）之间具有多对一关系，因此您需要在类中定义FK并从.PersonWorkGroupworkgroup_idPersonmembers_idmembersWorkGroup

在这些更改之后，我遇到了CircularDependencyError异常，很可能是由于prevPairings_idFK指向同一行。添加post_update=True到prevPairings关系解决了这个问题。

因此，以下是您需要执行的所有修复，以使您的代码正常工作：

class Person(db.Model):
    # ...
    workgroup_id = db.Column(db.Integer, db.ForeignKey('workgroup.id'))
    # No need to set uselist=False, it will be determined automatically by
    # type of relationship (many-to-one in this case).
    workGroup = db.relationship("WorkGroup", backref='members')
    # ...
    prevPairings = db.relationship('Person', post_update=True)
    # ...

class WorkGroup(db.Model):
    # ...
    # Removed members_id and members.
    # ...
于 2013-01-03T19:30:32.123 回答