[ZODB-Dev] listener on persistent objects

[Dieter Maurer]

heiko hees wrote at 2003-4-23 22:56 +0200:
 > we seek to implement an application, which allows external apps to to 
 > receive events on object change (w/o ZEO).
 > since the Persistent-class already tracks object changes, we assume, 
 > there must be a hook to be notified if any object change occures. any 
 > hints on using this hook?

It has been "__setattr__" but I think Jim made it now internal to
"Persistent". However, you may still use "__setattr__".

Note, that "__setattr__" is a bit prone to infinite loops.
You must assign to "__dict__" to avoid recursion.

 > further we need to determin all parents (objects referencing) of a 
 > certain Persistent-instance. gc.get_referers([obj]) doesn´t seem to work.

ZODB does not maintain this information.

Your application must do it when it has a need.

 > and finally it would be great if we could access a Persistent-instance 
 > by OID.

That's easy:

  If "o" is a persistent objects (already stored in ZODB),
  then "o._p_jar" is its ZODB connection reference.

  If "c" is a ZODB connection, then "c[oid]" returns the
  object with "oid" (or a POSKeyError, if no such object exists).


Dieter