[ZODB-Dev] Re: Getting an up to date instance of a persistent object

[Florent Guillaume]

Pascal Peregrina wrote:
> Hi,
> 
> I have a question regarding what triggers the reloading of an object
> state from ZODB (in order to set the most up to date one).
> 
> (note that I use ZEO)
> 
> Say you have C1, a Connection, and you have already retrieved object O1
> (so O1 is in C1 cache).
> Then, O1 is modified by something (that uses a different Connection).
> 
> When you reuse C1 and access O1, I would like to know what makes sure
> the O1 state is up to date.

Let's say C2 modified the same object. At C2 commit time, tpc_finish calls 
self._db.invalidate of all objects that C2 modified. Through a series of 
callbacks (involving ZEO also if used), this notifies all other connections 
through their invalidate() method that this object is invalidated. 
C1.invalidate() records that fact, and at C1 commit time there will be a 
conflict error if O1 is modified while also flagged invalidated by another 
connection.

Florent

> 
> Apparently, accessing O1._p_serial before anything else returns the old
> serial (so the latest state has not been set). I also tried C1.sync()
> (through O1._p_jar) before accessing O1._p_serial but I got same result.
> 
> And apparently, accessing O1._p_mitme before anything else does return
> the latest mtime and then accessing O1._p_serial does return the latest
> serial (so the latest state has been set)
> 
> Is that right? What's the rule?
> 
> Thanks for your help.
> 
> Pascal
> 
> 
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Florent Guillaume, Nuxeo (Paris, France)   Director of R&D
+33 1 40 33 71 59   http://nuxeo.com   fg at nuxeo.com