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的以前的经历和他们感兴趣的经历，并将它们链接到用户。我有一个匹配函数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。

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())

“匹配”路线中使用的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

这是一个非常小的示例，它再现了该错误：

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

哪个加薪：

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，在官方文档中，here是一个很好的资源来帮助您了解它们的工作方式。关键要点是它们处理其他ORM对象。因此，在查询关系时，需要提供一个ORM对象。在上面的示例中，如果将以下行：s.query(Child).filter_by(parent='a string').first()替换为以下行：s.query(Child).filter_by(parent=parent).first()，则错误消失了，因为parent是ORM对象。

在您的特定情况下，错误来自以下行：curr = prevExp.query.filter_by(user=user).first().expDescription，您将变量user传递给filter_by()方法。 user定义在user = prevExp.query.filter_by(user=current_user).first().expDescription上方的行中，在其中查询prevExp对象，并使用first()检索对象后，便可以访问其expDescription属性。 expDescription的列定义为expDescription = db.Column(db.String(400))：一个字符串。因此，您要传递一个str来查询关系属性，并创建上面的简化示例所演示的确切情况。

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。由于关系属性仅用于表示其他ORM对象，因此sqlalchemy假定您传入的字符串是ORM对象，而无需费心检查（为什么？！）。字符串没有_sa_instance_state属性，因此没有AttributeError。