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跟踪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，但它给出了标题中列出的属性错误。

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：

@app.route('/register', methods=['GET', 'POST'])
def register():
    form = RegistrationForm()
    if form.validate_on_submit():
        user = User(firstName=form.firstName.data, lastName=form.lastName.data,
                    username=form.username.data, email=form.email.data)
        user.set_password(form.password.data)
        db.session.add(user)
        db.session.commit()
        flash('Congratulations, you are now a registered user!')
        return redirect(url_for('login'))
    return render_template('register.html', form=form)

@app.route('/profile/edit/', methods=['GET', 'POST'])
@login_required
def editProfile():
    form = ProfileForm(obj=current_user)
    if form.validate_on_submit():
        previous = prevExp(user=current_user)
        previous.arts = form.prevArts.data
        previous.consulting = form.prevConsulting.data
        previous.dataScience = form.prevDataScience.data
        previous.education = form.prevEducation.data
        previous.engineering = form.prevEngineering.data
        previous.finance = form.prevFinance.data
        previous.government = form.prevGovernment.data
        previous.law = form.prevLaw.data
        previous.management = form.prevManagement.data
        previous.management = form.prevMarketing.data
        previous.medical = form.prevMedical.data
        previous.technology = form.prevTechnology.data
        previous.expDescription = form.expDescription.data
        interested = interestedExp(user=current_user)
        interested.arts = form.arts.data
        interested.consulting = form.consulting.data
        interested.dataScience = form.dataScience.data
        interested.education = form.education.data
        interested.engineering = form.engineering.data
        interested.finance = form.finance.data
        interested.government = form.government.data
        interested.law = form.law.data
        interested.management = form.management.data
        interested.marketing = form.marketing.data
        interested.medical = form.medical.data
        interested.technology = form.technology.data
        db.session.commit()
        flash('Your information has been saved!')
        return redirect(url_for('profile', username=current_user.username))
    return render_template('editProfile.html', form=form) 

@app.route('/matches')
@login_required
def matches():
    match = bestMatch()
    if match == None:
        message = "Sorry, there are no matches at this time. \
                   Please check back later!"
    else:
        message = "We've found a match for you! Check out "
    return render_template('matches.html', message=message, 
                           match=User.query.filter_by(username=match).first())

'match' 路由中使用的 bestMatch 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'

EDIT2：__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

这是一个重现错误的非常小的示例：

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

引发：

Traceback (most recent call last):
  File "55876558.py", line 27, in <module>
    s.query(Child).filter_by(parent='a string').first()
  File "C:\Users\peter_000\.virtualenvs\test-_0Fb_hDQ\lib\site-packages\sqlalchemy\orm\query.py", line 1689, in filter_by
    for key, value in kwargs.items()]
  File "C:\Users\peter_000\.virtualenvs\test-_0Fb_hDQ\lib\site-packages\sqlalchemy\orm\query.py", line 1689, in <listcomp>
    for key, value in kwargs.items()]
  File "C:\Users\peter_000\.virtualenvs\test-_0Fb_hDQ\lib\site-packages\sqlalchemy\sql\operators.py", line 344, in __eq__
    return self.operate(eq, other)
  File "C:\Users\peter_000\.virtualenvs\test-_0Fb_hDQ\lib\site-packages\sqlalchemy\orm\attributes.py", line 180, in operate
    return op(self.comparator, *other, **kwargs)
  File "C:\Users\peter_000\.virtualenvs\test-_0Fb_hDQ\lib\site-packages\sqlalchemy\orm\relationships.py", line 1039, in __eq__
    other, adapt_source=self.adapter))
  File "C:\Users\peter_000\.virtualenvs\test-_0Fb_hDQ\lib\site-packages\sqlalchemy\orm\relationships.py", line 1372, in _optimized_compare
    state = attributes.instance_state(state)
AttributeError: 'str' object has no attribute '_sa_instance_state'

Child.parent 是一个关系属性，官方文档中的here 是帮助您了解它们如何工作的好资源。关键的一点是它们处理其他 ORM 对象。因此，当您查询关系时，您需要提供一个 ORM 对象。在上面的示例中，如果您将这行：s.query(Child).filter_by(parent='a string').first() 替换为这行：s.query(Child).filter_by(parent=parent).first()，则错误消失，因为parent 是一个 ORM 对象。

在您的具体情况下，错误来自这一行：curr = prevExp.query.filter_by(user=user).first().expDescription，您将变量user 传递给filter_by() 方法。 user 在上面的行中定义，user = prevExp.query.filter_by(user=current_user).first().expDescription 在其中查询 prevExp 对象，一旦使用 first() 检索到它，您就可以访问它的 expDescription 属性。 expDescription 的列定义为expDescription = db.Column(db.String(400))：一个字符串。因此，您传递了 str 来查询关系属性并创建上面简化示例演示的确切情况。

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。由于关系属性纯粹用于表示其他 ORM 对象，sqlalchemy 假定您传入的字符串是 ORM 对象，而无需先检查（为什么会这样？！）。字符串没有_sa_instance_state 属性，因此没有AttributeError。