[Zope-Coders] Persistent Sessions question

[Evan Simpson]

This is primarily a question for Chris, but please chime in if you're 
familiar with <ominous echo>Mounting Databases</ominous echo>.

I'm setting up an application where Sessions will save me a lot of work, 
but I want to ensure that a user's session data doesn't just disappear 
in the middle of their, well, session.  In particular, data kept in 
temp_folder will go *poof* when I restart the server.

I don't want to keep sessions in the main ZODB, either, since they can 
change frequently and there will be a lot of them.  Also, I'm using ZEO. 
  Fun enough yet? ;-)

My solution seems to work, but I'm very nervous about it and want 
reassurance.  I set up ZEO to serve a 'Sessions.fs' FileStorage in 
addition to the normal 'Data.fs'.

I copied & hacked TemporaryFolder into a Product called MountedFolder. 
Here are the important guts from the MountedFolderMount class:

     def __init__(self, id, label):
         self.id = str(id)
         self.label = str(label)
         MountPoint.__init__(self, path='/',
                             params='Mountable %s' % self.label)

     def _createDB(self, db=None):
         """ Fetch the storage to mount from
             the Mountables dictionary in custom_zodb. """
         # We defer actually creating the Storage until it is needed.
         klass, args, kwargs = 
sys.modules['Zope.custom_zodb'].Mountables[self.label]
         db = DB(klass(*args, **kwargs))
         return db

     def _getMountRoot(self, root):
         sdc = root.get('folder', None)
         if sdc is None:
             sdc = MountedFolder()
             sdc.id = self.id
             sdc.storage_label_ = self.label
             root['folder'] = sdc
         return sdc

Now, I created a MountedFolderMount with label 'Session'. In my 
'custom_zodb.py', I created a dictionary called 'Mountables' with a 
single entry: the key is 'Session' and the value is a tuple consisting 
of ZEO.ClientStorage.ClientStorage, a tuple, and a dictionary containing 
the necessary arguments.  So, when the MountedFolderMount's _createDB is 
called, it instantiates a new ClientStorage and wraps it in a DB.

Having done all this, I created a Transient Object Container in the 
MountedFolder and set expiration to about a week.  I pointed my Session 
Data Manager at the new container, and everything *seems* to work as 
planned.

Thanks,

Evan