On May 7, 2008, at 2:29 PM, Laurence Rowe wrote:
When the generic address book application is built you don't know
what the departments will be called or indeed how many departments
there are. An address book is not be a great example, but I know of
intranet portal sites where this is a requirement. You want to
delegate control to each department so you give each department
their own instance of the portal. You only want to maintain one code
base though, and you don't want to change it every time someone adds
another departmental portal. I'd like to be able to create an add
form that has fields for application name and database url.
This probably seems like an odd requirement -- why not just run
multiple processes with different configurations -- but it's the way
zope has traditionally worked. A single process can serve multiple
instances of the same application (or `site`). When you get up to
running tens of sites, the memory footprint of Zope2 and Plone
(before the object cache) becomes significant.
If you are running different instances each connected to a different
engine within one process you wouldn't need any awareness of engines
at the object level (therefore no entity_name) and also no engine
proxying - you should have separate Session instances for each
"process" managed by scoped_session(), which was designed to handle
this. Multiple apps on one codebase within one process was an
original requirement of Pylons as well, though nobody has ever used it.
The easiest way to do it is to set up the engine at the request level:
Session = scoped_session()
# start of request
engine = get_appropriate_engine()
Session(bind=engine)
try:
# do request
finally:
Session.remove()
If that isnt granular enough, then you use a custom scope func which
maintains Session per-"process"-per-thread.
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