AttributeError:“str”对象没有属性“_sa_instance_state”

Question

我想评估链接到两个不同用户的值。我创建了一个不同的表来记录用户以前的体验和他们感兴趣的体验，并将它们与用户联系起来。我有一个匹配函数，它试图找到最相似的用户，但是它给出了标题中列出的属性错误。在

型号：

class User(UserMixin, db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(64), index=True, unique=True)
    prev = db.relationship('prevExp', backref='user', lazy='dynamic')
    interested = db.relationship('interestedExp', backref='user', 
                                 lazy='dynamic')
    matches = db.relationship('Match', backref='matchedTo', lazy='dynamic')

class prevExp(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    arts = db.Column(db.String(1))
    consulting = db.Column(db.String(1))
    dataScience = db.Column(db.String(1))
    education = db.Column(db.String(1))
    engineering = db.Column(db.String(1))
    finance = db.Column(db.String(1))
    government = db.Column(db.String(1))
    law = db.Column(db.String(1))
    management = db.Column(db.String(1))
    marketing = db.Column(db.String(1))
    medical = db.Column(db.String(1))
    technology = db.Column(db.String(1))
    expDescription = db.Column(db.String(400))
    userID = db.Column(db.Integer, db.ForeignKey('user.id'))

class interestedExp(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    arts = db.Column(db.String(1))
    consulting = db.Column(db.String(1))
    dataScience = db.Column(db.String(1))
    education = db.Column(db.String(1))
    engineering = db.Column(db.String(1))
    finance = db.Column(db.String(1))
    government = db.Column(db.String(1))
    law = db.Column(db.String(1))
    management = db.Column(db.String(1))
    marketing = db.Column(db.String(1))
    medical = db.Column(db.String(1))
    technology = db.Column(db.String(1))
    userID = db.Column(db.Integer, db.ForeignKey('user.id'))

class Match(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    person = db.Column(db.String(120))
    timestamp = db.Column(db.DateTime, index=True, default=datetime.utcnow)
    userID = db.Column(db.Integer, db.ForeignKey('user.id'))

路线：

^{pr2}$

“匹配”路由中使用的最佳匹配函数：

def bestMatch():
    curr = []
    curr.append(current_user)
    users = set(User.query.all()) - set(curr)
    existingMatches = set(Match.query.filter_by(matchedTo=current_user))
    users -= existingMatches 
    matchScore = dict()
    for user in users:
        username, score = countSimilarities(user)
        matchScore[username] = score
    scores = matchScore.values()
    bestScore = max(scores, default=0) if max(scores, default=0) > 0 else -1
    return matchScore.get(bestScore, None)

def countSimilarities(user):
    score = 0
    if user.major == current_user.major:
        score += 1
    score += countCollege(user.college, current_user.college)
    score += countHobbies(user.hobbies, current_user.hobbies)
    score += countPrevToInterested(user)
    score += countExpDescription(user)
    return user.username, score

def countExpDescription(user):
    user = prevExp.query.filter_by(user=current_user).first().expDescription
    curr = prevExp.query.filter_by(user=user).first().expDescription
    user = set(user.split(' '))
    curr = set(curr.split(' '))
    return len(user.intersection(curr))

编辑：错误：

File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 2309, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 2295, in wsgi_app
    response = self.handle_exception(e)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1741, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/flask_login/utils.py", line 261, in decorated_view
    return func(*args, **kwargs)
  File "/Users/gracekim/Desktop/projects/coffeechat/app/routes.py", line 96, in matches
    match = bestMatch()
  File "/Users/gracekim/Desktop/projects/coffeechat/app/matching.py", line 13, in bestMatch
    username, score = countSimilarities(user)
  File "/Users/gracekim/Desktop/projects/coffeechat/app/matching.py", line 26, in countSimilarities
    score += countExpDescription(user)
  File "/Users/gracekim/Desktop/projects/coffeechat/app/matching.py", line 52, in countExpDescription
    curr = prevExp.query.filter_by(user=user).first().expDescription
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 1792, in filter_by
    for key, value in kwargs.items()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 1792, in <listcomp>
    for key, value in kwargs.items()
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sqlalchemy/sql/operators.py", line 365, in __eq__
    return self.operate(eq, other)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sqlalchemy/orm/attributes.py", line 211, in operate
    return op(self.comparator, *other, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sqlalchemy/orm/relationships.py", line 1093, in __eq__
    other, adapt_source=self.adapter
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/sqlalchemy/orm/relationships.py", line 1466, in _optimized_compare
    state = attributes.instance_state(state)
AttributeError: 'str' object has no attribute '_sa_instance_state'

编辑2:__init__.py

from flask import Flask
from config import Config
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
from flask_login import LoginManager

app = Flask(__name__)
app.config.from_object(Config)
db = SQLAlchemy(app)
migrate = Migrate(app, db)
login = LoginManager(app)
login.login_view = 'login'

from app import routes, models

Answer 1

下面是一个非常小的示例，它再现了错误：

class Parent(Base):
    id = sa.Column(sa.Integer, primary_key=True)
    child = relationship('Child', backref='parent')


class Child(Base):
    id = sa.Column(sa.Integer, primary_key=True)
    parent_id = sa.Column(sa.Integer, sa.ForeignKey('parent.id'))


if __name__ == '__main__':
    Base.metadata.drop_all(engine)
    Base.metadata.create_all(engine)
    parent = Parent()
    child = Child(parent=parent)
    s = Session()
    s.add(parent)
    s.commit()
    s.query(Child).filter_by(parent='a string').first()  # this line causes error

这引发了：

^{pr2}$

Child.parent是一个关系属性，在正式文档中，here是帮助您理解它们是如何工作的一个很好的资源。关键的收获是它们处理其他ORM对象。因此，当您查询一个关系时，您需要提供一个ORM对象。在上面的示例中，如果您将这一行：s.query(Child).filter_by(parent='a string').first()替换为这行：s.query(Child).filter_by(parent=parent).first()，错误就会消失，因为parent是一个ORM对象。在

在您的特定情况下，错误来自于这一行：curr = prevExp.query.filter_by(user=user).first().expDescription，在这里您将一个变量user传递给filter_by()方法。user定义在上面的一行，user = prevExp.query.filter_by(user=current_user).first().expDescription在这里，您可以查询一个prevExp对象，一旦使用first()检索到它，您就可以访问它的expDescription属性。expDescription的列定义是expDescription = db.Column(db.String(400))：一个字符串。因此，您将传递一个str来查询relationship属性，并创建上面的简化示例所演示的确切情况。在

出现错误消息AttributeError: 'str' object has no attribute '_sa_instance_state'的原因是每个ORM对象都有一个_sa_instance_state属性。由于关系属性纯粹是用来表示其他ORM对象的，sqlalchemy假设传入的字符串是一个ORM对象，而不必先检查（为什么会这样？！）。字符串没有_sa_instance_state属性，因此AttributeError。在