SQLAlchemy对象已附加到会话

Question

我正在尝试为应用程序运行服务器,但我在登录时遇到错误:

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

我正在添加的会话似乎已经存在于数据库中.这是导致问题的代码片段:

@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)

正如您所看到的,我在尝试添加任何内容之前从会话表中打印内容,它是空的!([])

还有什么可能导致这个？

这是"会话"实施:

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

您尝试修改的对象已附加到另一个会话.也许您输入错误,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)

Answer 2

正如@marcinkuzminski所提到的,您无法添加已附加到另一个会话的对象.object_session()但是,如果您不确定会话是否源自您当前正在操作的相同线程上下文,那么从对象中拉入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 3

此错误意味着您正在处理的记录附加到 2 个不同的会话 ( db)！

原因之一是您可以使用一个定义模型并使用db = SQLAlchemy(app)另一个添加/插入/修改数据库！

我的解决方案是统一数据库！

尝试这个：

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 4

如果您要相互导入server.py和model.py，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L1到L5行，并将其放置在settings.py之类的通用文件中，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