[devel at bb.net] Adding attribute to serialized objects

[Dustin J. Mitchell]

That's tricky -- once you load and re-save a pickle with persistence
version N, code that doesn't have that version defined (older code) will
not be able to load the pickle.  So you'll need to apply the patch to all
instances.

Pickles are no fun :(

Dustin

On Tue, Jan 26, 2016 at 4:04 AM, Maria Marcano <mariangemarcano at gmail.com>
wrote:

> Hi,
>
> Do you know how we should handle adding an attribute to serialized object.
>
> We are doing some customizations and we would like to add content_type to
> class HTMLLogFile(styles.Versioned, LogFile):
>
> so we increased the
>
> persistenceVersion = 2
> and added the
>
> def upgradeToVersion2(self):
> self.content_type = ''
> self.wasUpgraded = True
>
> But we got an error if we want to run buildbot on a different branch that
> uses persistenceVersion = 1
>
> the exception is thrown from this library
> twisted/persisted/styles.py:400 in versionUpgrade
> assert persistVers <=  currentVers, "Sorry, can't go backwards in time."
>
> Do you know how this should be handled?, it looks like we are missing/not
> handle something?
>
> Thanks!
> Maria
>
>
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