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()
>
>
> >
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