I see. Would it be bad design to give an SA class instance a session
attribute or something similar? Not having it limits some work on that
object to the current scope. Consider this:
import util
from sqla_classes import TestClass
session = create_session(...)
obj = session.query(TestClass).select()[0]
util.doStuff(obj)
The doStuff method of util does not have access to session unless passed
explicitly. It would be convenient if obj knew what session it was a
part of. Maybe that would introduce some problems. I don't know.
Unless it has been detached, it should be in a session.
I frequently find myself wanting to get the session or engine from an SA
class instance because it's inconvenient or difficult to get the session
or engine otherwise and I don't want to make my code dependent on how
the connection is implemented. For example, this
class_mapper(someclass).mapped_table.metadata.engine
will only succeed if I connected metadata to the engine. I may decide
part way through a project to connect via create_session(bind_to=engine)
and my code would break.
Randall
Michael Bayer wrote:
> if you dont have a session to work with then youd just use
> connections off the engine being used.
>
> if you have your engines bound to tables and you want to get at that
> via the mapped class, first off id say why not just have the engine
> by itself somewhere? but if you really need to, it looks like
>
> class_mapper(someclass).mapped_table.metadata.engine
>
> for some examples about how to mix connections/sessions/transactions,
> see
>
> http://www.sqlalchemy.org/docs/unitofwork.myt#unitofwork_transaction
> http://www.sqlalchemy.org/docs/unitofwork.myt#unitofwork_transaction_sql
> http://www.sqlalchemy.org/docs/
> unitofwork.myt#unitofwork_transaction_using
>
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