Question

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

1. 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

Answer 1

This cannot be seen in your code, but I assume that the code that is executed twice is also executed within two different sessions. This would explain all the side effects you observe:

• only one address: because second session is not aware of the first one (not commit-ed)
• address ID is increased: this happens because of flush() in the first session where the identifier is assigned to the object. This is not an update to the previous Address though, but rather an ID assignment to the new Address.