SQLAlchemy 对象已附加到会话

Question

我正在尝试让应用程序运行的服务器，但我在登录时遇到错误：

[!] Object '<User at 0x7f12bc185a90>' is already attached to session '2' (this is '3')

看来我要添加的会话已经在数据库中了。这是导致问题的代码的 sn-p：

@app.route('/login', methods=['POST'])
def login():
    u = User.query.filter(User.username == request.form["username"]).first()
    if not u or u.password != request.form["password"]:
        return error("E1")

    s = Session.get_by_user(u)
    if s is not None:
         db_session.delete(s)
         db_session.commit()

     print db_session.execute("SELECT * FROM sessions").fetchall()

     s = Session(u)
     db_session.add(s)
     db_session.commit()

     return jsonify(s.values)

如您所见，在尝试添加任何内容之前，我正在打印会话表中的内容，但它是空的！ ([])

还有什么可能导致这种情况？

这里是“会话”的实现：

class Session(Base):
__tablename__ = "sessions"
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey('users.id'), unique=True)
user = relationship(User)
key = Column(String(50), unique=True)
created = Column(DateTime)

def __init__(self, user=None):
    self.user = user
    self.key = base64.encodestring(os.urandom(24)).strip()
    self.created = datetime.now()

def __repr__(self):
    return '<Session %r>' % (self.key)

@property
def values(self):
    return {"username" : self.user.username,
            "key" : self.key,
            "created" : str(self.created),
            }
@classmethod
def get_by_key(cls, key):
    s = cls.query.filter(cls.key == key).first()
    #print datetime.now() - s.created
    if s and datetime.now() - s.created > settings.SESSION_LIFETIME:
        s = None
    return s

@classmethod
def get_by_user(cls, user):
    s = cls.query.filter(cls.user == user).first()
    if s and datetime.now() - s.created > settings.SESSION_LIFETIME:
        s.query.delete()
        db_session.commit()
        s = None
    return s

Answer 1

此错误表示您正在处理的记录附加到 2 个不同的会话（db）！

其中一个原因是您可以使用一个 db = SQLAlchemy(app) 定义您的模型并使用另一个添加/插入/修改数据库！

我的解决方案是统一数据库！

试试这个：

u = db.session.query(User).filter(User.username == request.form["username"]).first()

而不是这个：

u = User.query.filter(User.username == request.form["username"]).first()

Answer 2

我也有这个问题。 我创建了一个 test_file.py 并添加了以下代码：

from app import app
from models import Tovar  
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy(app)

tovardel = Tovar.query.filter(Tovar.region == 1 and Tovar.price == 12).first()
db.session.delete(tovardel)
tovar = Tovar.query.filter(Tovar.region == 1 and Tovar.price == 12).first()
print(tovar.description)

当我运行代码时，我得到了这个错误：

Object '<Tovar at 0x7f09cbf74208>' is already attached to session '1' (this is '2')

问题解决：

如果您在例如 text_file.py 和 app.py 中有 db = SQLAlchemy(app)，那么您总是会遇到这个问题。你应该删除db = SQLAlchemy(app)，并从应用from app import db导入db

Answer 3

正如@marcinkuzminski 提到的，您不能添加已经附加到另一个会话的对象。但是，如果您不确定该会话源自您当前正在操作的同一线程上下文，那么仅使用 object_session() 从对象中提取原始会话是有风险的。线程安全的方法是使用 merge() ：

    local_object = db_session.merge(original_object)
    db_session.add(local_object)
    db_session.commit()

Answer 4

如果您让 server.py 和 model.py 相互导入，则会出现此数据库会话问题

server.py

from flask import Flask
import os
import models as appmod #################### importing models here in server.py<----------

app = Flask(__name__)                                  # L1
app.config.from_object(os.environ['APP_SETTINGS'])     # L2
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False   # L3
database = SQLAlchemy(app)                             # L4
db = database                                          # L5

@app.route('/item_delete/<id>', methods=['DELETE'])
def remove_method(id = None):
    data_rec = appmod.Employee.query.get(id)    
    db.session.delete(data_rec)
    db.session.commit()
    return "DELETE"

if __name__ == '__main__':

    app.run(port=5000, host='0.0.0.0',debug=True,threaded=True)

models.py

from server import db #################### importing server in models.py here <------------
from sqlalchemy.dialects.mysql import JSON


class Employee(db.Model):
    __tablename__ = 'employe_flask'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128))
    datetime = db.Column(db.DateTime)
    designation = db.Column(db.String(128))


    def __init__(self, name, datetime, designation):
        self.name = name
        self.datetime = datetime
        self.designation = designation

    @staticmethod
    def delete_rec(data_rec):
        db.session.delete(data_rec)#.delete
        db.session.commit()

    def __repr__(self):
        record = {"name":self.name,"date":self.datetime.ctime(),"designation":self.designation}.__str__()
        return record

从 server.py 中删除行 L1 到 L5 并将其放置在通用文件中，如 settings.py 并将'app'和'db'导入server.py并在models.py中导入db

喜欢下面的文件

server.py

from flask import Flask
import os
import models as appmod 
from settings import app, db


@app.route('/item_delete/<id>', methods=['DELETE'])
def remove_method(id = None):
    data_rec = appmod.Employee.query.get(id)    
    db.session.delete(data_rec)
    db.session.commit()
    return "DELETE"

if __name__ == '__main__':

    app.run(port=5000, host='0.0.0.0',debug=True,threaded=True)

settings.py

import os
from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)                                  # L1
app.config.from_object(os.environ['APP_SETTINGS'])     # L2
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False   # L3
database = SQLAlchemy(app)                             # L4
db = database                                          # L5

models.py

from settings import db
from sqlalchemy.dialects.mysql import JSON


class Employee(db.Model):
    __tablename__ = 'employe_flask'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128))
    datetime = db.Column(db.DateTime)
    designation = db.Column(db.String(128))


    def __init__(self, name, datetime, designation):
        self.name = name
        self.datetime = datetime
        self.designation = designation

    @staticmethod
    def delete_rec(data_rec):
        db.session.delete(data_rec)#.delete
        db.session.commit()

    def __repr__(self):
        record = {"name":self.name,"date":self.datetime.ctime(),"designation":self.designation}.__str__()
        return record

Answer 5

您尝试修改的对象已附加到另一个会话。 也许你有错误的导入，而 db_session 是一个新实例。

一个很好的解决方法是提取当前绑定的会话并使用它：

代替：

db_session.add(s)

做：

current_db_sessions = db_session.object_session(s)
current_db_sessions.add(s)