KeyError：*在使用SQLAlchemy在Flask上运行db.session.add时，实际上是一个很大的数字*

Question

我有一个User类：

class User(db.Model, UserMixin):
    """
    ORM Class: An object that represents a user
    """
    __tablename__ = "Users"
    id              = db.Column('id',           db.Integer,             primary_key=True)
    email           = db.Column('email',        db.String(128),         unique=True)
    passwordhash    = db.Column('passwordhash', db.String(128))

def __init__(self, email, password):
    self.email = email
    self.passwordhash = generate_password_hash(password)

    logging.info("creating user with email and pw:" + email + " " + password)

当我创建新用户时：

newuser = User(email="test@email.com", password="hunter2")
db.session.add(newuser)

我得到一个KeyError：140736669950912

  File "/usr/local/lib/python3.6/site-packages/sqlalchemy/util/_collections.py", line 988, in __call__
    return self.registry[key]
KeyError: 140736669950912

这个号码来自哪里？我在处理KeyError期间也遇到了另一个错误，即RuntimeError: application not registered on db instance and no applicationbound to current context

Answer 1

根据current documentation的建议， 而不是手动创建SqlAlchemy()的实例并将其保存到db，尝试继承sqlalchemy.ext.declarative.Base，如下所示：

from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine(DATABASE_URI, echo=False)
db_session = scoped_session(sessionmaker(autocommit=False, autoflush=False, bind=engine))

Base = declarative_base()
Base.query = db_session.query_property()


# the following should be moved to your models.py

from sqlalchemy import Column, Integer, String

class User(Base):
    """ORM Class: An object that represents a user
    """
    __tablename__ = "Users"

    id = Column(Integer)
    email = Column(String(128), primary_key=True)
    passwordhash = Column(String(128), unique=True)

Answer 2

检查您的迁移是否最新也可能有所帮助。当我遇到此问题时，在删除现有迁移并重新运行迁移后，该问题已得到解决：

python manage.py db migrate
python manage.py db ugrade