在 Sqlalchemy 中，在类关系属性中附加对象两次时出现奇怪的行为

发布于 2024-12-10 15:45:45 字数 1345 浏览 0 评论 0原文

我在学习 SQLAlchemy 时遇到一些奇怪的问题。我正在使用它的0.7.2版本。这些是我的测试类：

    class User(Base):
        __tablename__ = 'users'

        id = Column('user_id',Integer,primary_key = True)
        name = Column('user_name',String(20))

        addresses = relationship("Address",backref="user")

        def __repr__(self):
              return "<User(%s)>" % self.name

    class Address(Base):
          __tablename__ = 'addresses'

          id = Column('adress_id',Integer,primary_key = True)
          address = Column('address',String(30))
          user_id = Column('user_id',ForeignKey('users.user_id'))

          def __repr__(self):
               return "<Address(%s)>" % self.address

我不小心运行了主文件两次，这使得以下代码运行了两次

会话 = sessionmaker()
会话=会话（绑定=引擎）
q=session.query(用户)
a=q.get(3)
a.addresses.append(地址(address='myaddress'))
会话.flush()
打印a.addresses[0].id,a.addresses[0].address

我最初认为 a.addresses 会有两个带有“myaddress”的地址对象。但实际上只有一个对象的address_id被更新了。我的意思是说，当我首先运行文件时，它打印了

1,'我的地址'

然后在第二次运行时打印

2、'我的地址'

我通过打印 a.addresses 确认仅存在 Address 对象，并且它只显示其中的对象。

难道它不应该在追加时在 a.addresses 中添加第二个 Address 对象，而不是更新现有地址对象的 id 吗？

请注意，没有执行 session.commit() 命令。我只是运行该文件两次并注意到了这种行为。

编辑：添加了创建新会话并负责解决问题的代码，如下面答案中 van 所建议的那样

原文

I am facing some odd problems while learning SQLAlchemy. I am using 0.7.2 version of it. These are my test classes:

    class User(Base):
        __tablename__ = 'users'

        id = Column('user_id',Integer,primary_key = True)
        name = Column('user_name',String(20))

        addresses = relationship("Address",backref="user")

        def __repr__(self):
              return "<User(%s)>" % self.name

    class Address(Base):
          __tablename__ = 'addresses'

          id = Column('adress_id',Integer,primary_key = True)
          address = Column('address',String(30))
          user_id = Column('user_id',ForeignKey('users.user_id'))

          def __repr__(self):
               return "<Address(%s)>" % self.address

I accidentally ran my main file twice which made following code run twice
```
Session = sessionmaker()
session = Session(bind=engine)
q=session.query(User)
a=q.get(3)
a.addresses.append(Address(address='myaddress'))
session.flush()
print a.addresses[0].id,a.addresses[0].address
```
I initially thought that a.addresses would have got two address object with 'myaddress'. But actually there is only one object whose address_id got updated. I mean to say when I ran file first it printed
```
1,'myaddress'

and then in second run it printed

2,'myaddress'
```

I confirmed existence of only Address object by printing a.addresses and it shows only object in it.

Should it not add a second Address object in a.addresses on append instead of updating id of existing address object?

Note there is no session.commit() command executed. I simply ran the file twice and noticed this behaviour.

Edit : Added code which creates new session and is responsible for the problem as suggested by van below in the answer

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