[Zope3-dev] class lifecycle management/missing attributes

[Peter Simmons]

Opps that should have been

why is an upgrade script like Tres is suggesting not suitable?

Peter Simmons wrote:

> Hi,
>
> Just out of interest why is an upgrade script like Tres is suggesting?
>
> We schedule upgrades so that users aren't using the system, is that 
> not possible for your system?
>
> I figure there is a good reason but I can't think of it and was 
> wondering.
>
> Cheers,
> Pete
>
> Garrett Smith wrote:
>
>> Tres Seaver wrote:
>>  
>>
>>> __setstate__ hackery can work, but is fragile:  because the object is
>>> not marked as modified when changed by __setstate__, it doesn't get
>>> persisted in the upgraded state.  Write-on-read has scalability
>>> problems, as well, which also tend to make 'mutate inside an accessor'
>>> solutions unsatisfactory.
>>>   
>>
>>
>> I view a 'deserialize' operation as a constructor proxy -- very much a
>> write operation.
>>
>> Is __setstate__ the Persistence deserialize method? Can't _p_changed be
>> set in that method?
>>
>>  
>>
>>> Our usual practice in the case where a class-scope default won't work
>>> is to write a script which trolls through the ZODB, converting wayward
>>> objects as it find them.  Such scripts keep the cruft in ancillary
>>> code;  not only that, one can typically discard the scripts after
>>> having run them against each affected ZODB.
>>>   
>>
>>
>> I can see an approach like this for a RDB, given their infrastructure
>> for schema management and evolution. But...yikes...what do you tell
>> users who get to the unconverted objects before the script does?
>>
>>  
>>
>>> Persistence-means-never-being-able-to-forget-your-mistakes'ly,
>>>   
>>
>>
>> Aw...that's not very XPish of persistence ;-)
>>
>> On the more extreme side, isn't there an ZODB upgrade strategy for
>> product revisions?
>> -- Garrett
>>
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>>
>>
>>  
>>
>

-- 
Peter Simmons
Senior Consultant                  BCMPweb Limited
+64 21 676 909                      +64 9 267 4676
pete@bcmpweb.com            http://www.bcmpweb.com