[ZODB-Dev] Persistent object has empty __dict__ for a little while

[Tres Seaver]

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Martin Aspeli wrote:
> Hi,
> 
> This one is pretty high no the list of weirdest things to have happened 
> to me in a while. Basically, I have a persistent object that has an 
> empty __dict__() on the first request, until it suddenly decides to have 
> data again.
> 
> I'm on ZODB 3.9.3, using Zope 2.12 and Plone 4. I have a persistent 
> object, /plone/portal_registry:
> 
>    class Registry(registry.Registry, SimpleItem):
>        pass
> 
> The base class is:
> 
>    class Registry(Persistent):
>        def __init__(self):
>            self._records = Records(self)
> 
> Records is:
> 
>      class Records(Persistent):
> 
>        __parent__ = None
> 
>        def __init__(self, parent):
>            self.__parent__ = parent
>            self.data = OOBTree()
> 
>        def __getitem__(self, name):
>            return self.data.__getitem__(name)
> 
> The BTree contains string keys and Record objects as values. Record is:
> 
>      class Record(Persistent):
>          __name__ = u""
>          __parent__ = None
> 
>          field = None
> 
> __parent__ is set to records.__parent__, which is going to be the 
> Registry object.
> 
> field is set to a special persistent field class inheriting from 
> zope.schema's fields, but mixing in persistence. In this case, I have a 
> list field:
> 
>    class PersistentField(persistent.Persistent):
>        """Base class for persistent field definitions.
>        """
> 
>    class PersistentCollectionField(PersistentField,
>               zope.schema._field.AbstractCollection):
> 
>    class List(PersistentCollectionField, zope.schema.List):
>        pass
> 
> I then have some code like this:
> 
>      def cloneField(self, field):
>          clone = field.__class__.__new__(field.__class__)
>          clone.__dict__.update(field.__dict__)
>          for name, attr in field.__dict__.items():
>              if IField.providedBy(attr):
>                  clone.__dict__[name] = self.cloneField(attr)
>          return clone
> 
> This is used like so:
> 
>      registry = getUtility(IRegistry) # persistent/local
>      clone = self.cloneField(registry.records[recordName].field)
> 
> This seems to work always *except* on the first request immediately 
> after starting up Zope. In this case, field.__dict__ is {}. If I poke at 
> it long enough in pdb, it suddenly springs into life and contains values 
> again.
> 
> Can anyone enlighten me as to:
> 
>   - why this may happen
>   - how I can ensure it stops happening :-)

You have a ghost, likely:  try getting it to unghostify by accessing an
attribute, or calling '_p_activate' (accessing '__dict__' doesn't
provoke the auto-activation).


Tres.
- --
===================================================================
Tres Seaver          +1 540-429-0999          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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