On Oct 18, 2011, at 1:21 PM, Manav Goel wrote:
> Hello,
> I am working in eclipse IDE.
> I have this code in the file :
>
>
> class User(Base):
> __tablename__ = 'users'
>
> id = Column('user_id',Integer,primary_key = True)
> name = Column('user_name',String(20))
>
> addresses = relationship("Address")
>
> def __repr__(self):
> return "<User(%s)>" % self.name
>
> session = Session(bind=engine)
> u=User('myname')
> session.add(u)
> session.flush()
> print u.id
>
> I ran this file and it worked fine but then I changed
> something.
> Now to see the effect I have to run file again and then I
> noticed this
>
> Instead of adding two different objects with two
> different ids but same name. It simply updated the id of already existing
> object.
>
> Now I have two questions :
>
> 1. What is the reason of this behavior? First of all it should have
> made two different objects .
absolutely. the User() object has no primary key assigned and is not the
result of a previous query, so add() will add it as a new row. So the code
above is not the complete story and you'd have to figure out what you're doing
on your end beyond what's illustrated above.
> But I think it did not do that because it thought this object is similar to
> existing one.
This is not SQLA's behavior. SQLAlchemy does not make guesses about data.
> In that case it should have raised exception instead of simply my primary key.
what kind of exception ? its legal to have two objects with the same name here
unless you applied a unique constraint to the "user_name" column which does not
seem to be the case here.
>
> 2. WHat happened when I ran the file again? It created a brand new
> session or continued the previous one?
The Session is an instantiation of an object present in memory only within the
Python process. So by definition any new invocation of a Python program begins
with all new state including Session objects.
>
> 3. Due to problem mentioned in point no 1. it wasted my early id nos
> as when I committed it saved the last one?
I don't know what this means.
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