[Grok-dev] Pickling an object stored in the Zodb. How do I skip the __parent__ attribute?

Sebastian Ware sebastian at urbantalk.se
Fri Aug 15 10:19:25 EDT 2008

I have succeeded in exporting a list of objects using an adapter to  
override __getstate__ for the root object. I have no references bellow  
the "root objects" (except __parent__ in each root object) so I don't  
have to worry about checking if objects are "outside" the branch that  
I am exporting. The code is basically the following:

   class IExportableObject(Interface):

   class ExportableObject(grok.Adapter):
       This adapter is used for the root object that I want to export.  
       removes the __parent__ reference from the __getstate__ dictionary
       thus stopping the the pickler from traversing bellow the root  
       in the object graph.

       def __getstate__(self):
           state = self.context.__getstate__()
           del state['__parent__']

           return state

and it is called from an export view that looks like this:

   class Export(grok.View):

     def update(self):
         import cPickle

         tmp = []
         for obj in self.context['default'].values():
             xobj = interfaces.IExportableObject(obj)
         self.exportdata = cPickle.dumps(tmp)

     def render(self):
         from tempfile import TemporaryFile
         exportfile = TemporaryFile('w')
         filename = self.context.__name__ + '.export'
         response = self.request.response
                            'attachment; filename=%s' % filename)
         response.setHeader('Content-Type', 'application/octet-stream')
         return exportfile

This exports the data including annotations. Now I am going to start  
working on the import :)

Mvh Sebastian

14 aug 2008 kl. 20.03 skrev Kevin Smith:

> Hi Sebastion,
> Please let me know if you make headway with this, I've tried a  
> number of things to make this work, without success.
> Thanks,
> Kevin Smith
> Sebastian Ware wrote:
>> Thanks for the pointer! I have read:
>>    http://www.python.org/dev/peps/pep-0307/
>> And found that the pickling is done by calling the method you refered
>> to:
>>    __getstate__()
>> and that it really does exist on the objects in the Zodb. I will
>> override the method by means of an adapter for the root object that I
>> am pickling and remove the attribute [__parent__]. Feels as though
>> this might actually work :)
>> Mvh Sebastian
>> 14 aug 2008 kl. 15.11 skrev Jegenye 2001 Bt (Miklós Prisznyák):
>>> 2008/8/14 Sebastian Ware <sebastian at urbantalk.se>
>>> I am trying to export and import objects from the Zodb using
>>> cPickle.dumps().
>>> My problem is that the pickler traverses the __parent__ attribute  
>>> thus
>>> returning a much larger object graph than I wish to serialize.
>>> Do I have to subclass the pickler or is there som other smart way of
>>> making it skip the __parent__ attribute?
>>> You could  write an adapter  (or modify the class of the content
>>> objects itself) to use __setstate__ and __getstate__ , etc:
>>> http://www.python.org/doc/2.5/lib/node321.html
>>> -- 
>>> Best regards,
>>>    Miklós
>>> _______________________________________________
>>> Grok-dev mailing list
>>> Grok-dev at zope.org
>>> http://mail.zope.org/mailman/listinfo/grok-dev
>> _______________________________________________
>> Grok-dev mailing list
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> <kevin.vcf>

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