[Sqlalchemy-tickets] Issue #4310: the behavior about session commit is unexpected in ORM!!! (zzzeek/sqlalchemy)

[Li G. <iss...@bi...>]

New issue 4310: the behavior about session commit is unexpected in ORM!!!
https://bitbucket.org/zzzeek/sqlalchemy/issues/4310/the-behavior-about-session-commit-is

Li GuangTian:

```
#!python

from sqlalchemy import Column, Integer, String
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

Base = declarative_base()


class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(16))
    password = Column(String(16))

    def __repr__(self):
        return "<User(name='%s', password='%s')>" % (
            self.name, self.password)


if __name__ == '__main__':
    engine = create_engine(
        'mysql+pymysql://',
        echo=False)
    Session = sessionmaker(bind=engine)
    session = Session()
    user = User(name="test", password="test")
    print(len(user.__dict__.keys()))  # 3
    session.add(user)
    print(len(user.__dict__.keys()))  # 3
    session.flush()
    print(len(user.__dict__.keys()))  # 4
    session.commit()
    print(len(user.__dict__.keys()))  # 1

    user = User(name="test", password="test")
    print(len(user.__dict__.keys()))  # 3
    session.add(user)
    print(len(user.__dict__.keys()))  # 3
    session.flush()
    print(len(user.__dict__.keys()))  # 4
    session.commit()
    id = user.id
    print(len(user.__dict__.keys()))  # 4
```
The output seems that after session committed, the attribute of the object is not visible. But when you try to access any attribute, the behavior is excepted.