Re: [ZODB-Dev] Setting the jar
Tim Peters wrote: ... add() is a relatively new API, intended to be called "by hand" when someone wants to force a new object to get an oid. I'm not really clear about the use case(s) that drove its addition, but it's not normally involved in auto-assigning oids and/or jars. add was originally added to support deriving hash keys from persistent objects based on their oids (and later database names). If we want to use a new persistent object as a key, based on it's persistent identity, we need to establish it's identity using add. A newer application of add is for resolving ambiguities when a new object if referenced from multiple databases. If you create a new object and reference it from multiple databases, then you'll get an error when you try to commit the transaction because ZODB can't tell which database to assign the object to. An application can use add before the commit to resolve this ambiguity. Jim P.S. No, I'm not back yet. :) -- Jim Fulton mailto:[EMAIL PROTECTED] Python Powered! CTO (540) 361-1714http://www.python.org Zope Corporation http://www.zope.com http://www.zope.org ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
RE: [ZODB-Dev] Setting the jar
[Florent Guillaume] >>> What part of the transaction/persistence code sets the _p_jar of a >>> persistent object to that of its parent when the object is assigned to >>> a persistent parent and transaction.commit(1) is called ? [Tim] >> I'm massively overloaded today, so it would really help if you could >> name the version of ZODB you're wondering about ;-). [Florent] > No problem, there's no hurry. > > Latest ZODB 3.4 would do (I'm maintly interested in Zope 2.8 here. > > I've seen something that look like what I want in > ZODB.Connection.Connection.add, but I can't see who calls it. add() is a relatively new API, intended to be called "by hand" when someone wants to force a new object to get an oid. I'm not really clear about the use case(s) that drove its addition, but it's not normally involved in auto-assigning oids and/or jars. > To be clear, I'm interested in how the _p_jar happens on a new object > that's just been created. Basically if you do: > > # folder is a persistent object that has a _p_jar > # folder.foo = Foo() # where Foo inherits from Persistent > # here folder.foo doesn't have a _p_jar > transaction.commit(1) > # here folder.foo has a _p_jar, how come ? > > I think I've missed something in my code trawling ;) Indeed, this will have you crawling on your belly for the next week . In effect, it all happens as a side effect of pickling, via the persistent_id() method of (in ZODB 3.4) class ZODB.serialize.ObjectWriter. The class docstring is telling the truth: """Serializes objects for storage in the database. The ObjectWriter creates object pickles in the ZODB format. It also detects new persistent objects reachable from the current object. """ but exactly how that happens requires tracing thru Python's C pickle code too. Stick a print or a breakpoint here (inside persistent_id()) and you can watch it happening: if oid is None: oid = obj._p_oid = self._jar.new_oid() obj._p_jar = self._jar self._stack.append(obj) Note that ObjectWriter is passed a single object, but Connection._store_objects iterates over the ObjectWriter instance. In your example, "folder.foo = Foo()" marks `folder` as changed, and the new object bound to .foo is discovered while pickling the new state for `folder`. Iterating over an ObjectWriter(obj) instance can end up discovering an arbitrarily large and complex graph of new objects reachable from obj, as it tries to pickle each in turn. That's what the `self._stack` in the above is keeping track of. ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
Re: [ZODB-Dev] Setting the jar
On 4 Aug 2005, at 22:11, Tim Peters wrote: [Florent Guillaume] What part of the transaction/persistence code sets the _p_jar of a persistent object to that of its parent when the object is assigned to a persistent parent and transaction.commit(1) is called ? I'm massively overloaded today, so it would really help if you could name the version of ZODB you're wondering about ;-). No problem, there's no hurry. Latest ZODB 3.4 would do (I'm maintly interested in Zope 2.8 here. I've seen something that look like what I want in ZODB.Connection.Connection.add, but I can't see who calls it. To be clear, I'm interested in how the _p_jar happens on a new object that's just been created. Basically if you do: # folder is a persistent object that has a _p_jar folder.foo = Foo() # where Foo inherits from Persistent # here folder.foo doesn't have a _p_jar transaction.commit(1) # here folder.foo has a _p_jar, how come ? I think I've missed something in my code trawling ;) Florent -- Florent Guillaume, Nuxeo (Paris, France) CTO, Director of R&D +33 1 40 33 71 59 http://nuxeo.com [EMAIL PROTECTED] ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
RE: [ZODB-Dev] Setting the jar
[Florent Guillaume] > Trying to understand some code... > > What part of the transaction/persistence code sets the _p_jar of a > persistent object to that of its parent when the object is assigned to a > persistent parent and transaction.commit(1) is called ? I'm massively overloaded today, so it would really help if you could name the version of ZODB you're wondering about ;-). ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
[ZODB-Dev] Setting the jar
Trying to understand some code... What part of the transaction/persistence code sets the _p_jar of a persistent object to that of its parent when the object is assigned to a persistent parent and transaction.commit(1) is called ? Florent -- Florent Guillaume, Nuxeo (Paris, France) CTO, Director of R&D +33 1 40 33 71 59 http://nuxeo.com [EMAIL PROTECTED] ___ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org http://mail.zope.org/mailman/listinfo/zodb-dev
