Binding different engines to a session object

[Andrew]

Hi:

I have been having problems in attempting to rebind a given Session
object/class to a different engine instance. It seems that it can only
be bound once. Subsequent sql statements post to the original binding.
I am using sqlalchemy 0.4.6 with elixir. Here is an example:


__session__ = scoped_session(sessionmaker(...))

Session.configure(bind=engine1)

# do sql ops here on engine1 via elixir

__session__.configure(bind=engine2)

# do sql ops here against engine2 via elixir
# sql ops here get written to database that engine1 is pointing to.


The 2 engines I am referring to have identical schemas in different
databases. In fact there may be multiple databases (with the same
schema) in which I need to set the database context before performing
sql operations. I thought the __session__.configure(bind=) would do
the trick but it doesn't seem to be working. Can anyone provide some
insight into how I can use sqlalchemy to write to multiple databases
with the same schema? As shown this app is multithreaded (zope). I
have received some advice to create a new session instance per schema
(eg: sess=Session()) however elixir only refers to a single session
object/class (__session__) which makes things difficult. Do I need to
dump elixir and just use sqlalchemy to get this functionality?

Thanks!



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[Andrew]

I believe I have fixed my problem. Instead of binding/rebinding a
given engine instance to the Session, I bind to the metadata object.
This solves the problem instead. I found that there are numerous
references to being able to rebind metadata but not sessions.

Post by Andrew
I have been having problems in attempting to rebind a given Session
object/class to a different engine instance. It seems that it can only
be bound once. Subsequent sql statements post to the original binding.
__session__ = scoped_session(sessionmaker(...))
Session.configure(bind=engine1)
# do sql ops here on engine1 via elixir
__session__.configure(bind=engine2)
# do sql ops here against engine2 via elixir
# sql ops here get written to database that engine1 is pointing to.
The 2 engines I am referring to have identical schemas in different
databases. In fact there may be multiple databases (with the same
schema) in which I need to set the database context before performing
sql operations. I thought the __session__.configure(bind=) would do
the trick but it doesn't seem to be working. Can anyone provide some
insight into how I can use sqlalchemy to write to multiple databases
with the same schema? As shown this app is multithreaded (zope). I
have received some advice to create a new session instance per schema
(eg: sess=Session()) however elixir only refers to a single session
object/class (__session__) which makes things difficult. Do I need to
dump elixir and just use sqlalchemy to get this functionality?
Thanks!

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[Michael Bayer]

Post by Andrew
I have been having problems in attempting to rebind a given Session
object/class to a different engine instance. It seems that it can only
be bound once. Subsequent sql statements post to the original binding.
__session__ = scoped_session(sessionmaker(...))
Session.configure(bind=engine1)
# do sql ops here on engine1 via elixir
__session__.configure(bind=engine2)

this is the wrong approach. configure() binds the overall
scoped_session, which is not itself a session but rather a container
of many sessions as well as a factory for new sessions, to a new
engine which only takes effect upon the next creation of a Session.
configure() is only used for an application which would like to
establish a scoped_session but does not yet have an available engine.

To bind a single session to an engine, simply assign the "bind"
attribute:

mysession.bind = someengine

when using a scoped_session(), the current session is available by
calling it:

mysession = __session__()





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