Thanks for taking the time to answer this. I have had a frustrating
day and this gives me hope again, =)
I'm not trying to move objects between sessions.
I might be misunderstanding the APIs here, but what I think I need is
the following:
Two persons surf to my site at the same time and I keep some session-
specific data in an SQLite3 file.
One SQLite3 file per person/session.
(I know that CherryPy stores session info and I'm using it now, but
this part of the code was written before I understood that.)
So for each new person/session I instantiate the following class which
I then keep in memory through CherryPy session management.
class Session(object):
def __init__(self, name):
self.db = create_engine( 'sqlite:///%s' % name )
self.db.echo = False
self.metadata = BoundMetaData(self.db)
self.session = create_session()
self.db.docs = Table('docs', self.metadata, autoload=True)
self.db.mapper = mapper(Document, self.myDB.docs)
The second time I instantiate this class I get an error saying that
the class has already a primary mapper defined, which is true.
How do I go around this?
Thanks again!
On Jul 24, 4:47 pm, Michael Bayer <[EMAIL PROTECTED]> wrote:
> theres multiple levels of issues with this.
>
> one is, its not very clean to move objects between databases using
> sessions. to do so, you have to remove the "_instance_key" of the
> object and save it into the other session:
>
> f = Foo()
> sess1.save(f)
> sess1.flush()
>
> sess1.expunge(f)
> del f._instance_key
> sess2.save(f)
> sess2.flush()
>
> the second is, a mapper does not define *where* you are storing your
> object, it only defines *how*. therefore you *never* make a second
> mapper for a class, unless you are using one of two very specific
> recipes which are mentioned in the docs (which this example is not).
>
> third, the SessionContextExt shouldnt really "interfere" with this
> operation, in that it wont prevent you from expunging the object from
> one session and saving it into another, but it does make it
> confusing. SessionContextExt is just the tiniest little convenience
> feature, that of "your objects automatically get saved into a
> session" and also "lazy loaders know how to find a session". but if
> you are moving objects between sessions i would think its just going
> to confuse matters since its making decisions for you behind the
> scenes. i think its important to try to make your code work while
> using the minimal (minimal here meaning, "none") number of "add-ons"
> to start with, so that you have something which works and can be
> understood. then the add-ons can be implemented afterwards, as the
> need for them arises.
>
> On Jul 24, 2007, at 10:18 AM, alex.schenkman wrote:
>
>
>
> > Hi:
>
> > I'm new writing web apps and I'm using cherrypy with sqlalchemy.
> > As I understand it, each user navigating the site and clicking on
> > pages gets a new thread and thus it is necesary to use sqlalchemy in
> > a thread-safe manner.
>
> > After reading the docs I assume that I have to use SessionContextExt,
> > but I don't figure out how.
>
> > As a test I try to write records to two different databases, but I
> > always get a mapper error.
>
> > sqlalchemy.exceptions.ArgumentError: Class '<class '__main__.Doc'>'
> > already has a primary mapper defined with entity name 'None'.
>
> > Any hint is much appreciated!!
>
> > This is the code I try:
>
> > from sqlalchemy import *
> > from sqlalchemy.ext.sessioncontext import SessionContext
>
> > class Doc(object):
> > def __init__(self, id, path, state):
> > self.DocID = id
> > self.Path = path
> > self.Complete = state
>
> > if __name__ == "__main__":
> > db1 = create_engine( 'sqlite:///test.db' )
> > db1.echo = False
> > metadata = BoundMetaData( db1 )
> > docs = Table('docs', metadata, autoload=True)
>
> > ctx1 = SessionContext(create_session)
> > mapper(Doc, docs, extension=ctx1.mapper_extension)
> > d = Doc(43,'/etc/password',True)
> > ctx1.current.flush()
>
> > db2 = create_engine( 'sqlite:///test2.db' )
> > db2.echo = False
> > metadata2 = BoundMetaData( db2 )
>
> > d = Doc(15,'/etc/init',False)
>
> > ctx2 = SessionContext(create_session)
> > mapper(Doc, docs, extension=ctx2.mapper_extension)
> > ctx2.current.flush()
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~----------~----~----~----~------~----~------~--~---
