[Zope3-Users] Re: Evolution of ZoDB after changing python modules structure (moving content classes to another module)

[Marius Gedminas]

On Sun, Jun 10, 2007 at 09:14:24AM +0200, Aleksander Kowalczyk wrote:
> On 6/8/07, Alek Kowalczyk <thealx at poczta.onet.pl> wrote:
> >
> >Alek Kowalczyk <thealx at ...> writes:
> >
> >>
> >> Hi,
> >> I moved my content class from mypackage.mymodule.MyContentClass into
> >> mypackage.mysubpackage.mymodule.MyContentClass.
> >> But when started Zope and went to visit an object I have previously
> >created (of
> >> MyContentClass), I get:
> >> ComponentLookupError: ((<persistent broken
> >mypackage.mymodule.MyContentClass
> >> instance '\x00\x00\x00\x00\x00\x00\x02q'>,
> >> <zope.publisher.browser.BrowserRequest instance
> >
> I found a quite well working solution on
> >http://mail.zope.org/pipermail/zodb-dev/2006-September/010382.html
> >
> >There was only one issue: this solution assumes that we have given a DB,
> >while
> >Zope evolve method receives already open connection. Unfortunately
> >classFactory
> >from DB is cached in Connection's private fields in constructor.
> >Because of that I could not assign my custom 'renaming' class factory
> >using:
> >
> >def evolve(context): #won't work!
> >    context.connection.db().classFactory = myClassFactory
> >
> >Instead I had to do some dirty private fields substitution in Connection's
> >ObjectReader:
> >
> >def evolve(context): #this works nice
> >    context.connection._reader._factory = myClassFactory
> 
> 
> I shouldn't announce success too early. The solution works but only during
> first Zope run (i.e just after evolving the schema).
> Although classFactory returns proper class during evolve, the new class name
> is not saved in ZoDB, so after next unghosting object get old class names
> again.
> 
> Here is my evolve script. I really don't know what more should I do to make
> Zope/ZoDB write the new class name in ZoDB. Can someone help me a bit... :)
> ?
> 
> def convertingClassFactory(connection, moduleName, globalName):
>    #convert class name to new one and return the class object
> 
> def evolve(context):
>    #dirty hack to substitute classFactory
>    context.connection._reader._factory = convertingClassFactory
>    root = context.connection.root().get(ZopePublication.root_name, None)
>    for object in findObjectsMatching(root, lambda x: True):
>        if hasattr(object, '_p_activate'):
>            object._p_activate()
>            object._p_changed = True

Note that findObjectMatching will not return all the persistent objects,
but only those that are directly placed in containers.  Other objects
(e.g. ones stored in annotations) refer to your old classes, you'll need
to do more.  Stephan Richter once figured out how to do that for
SchoolTool, IIRC it involved looping through all OIDs in the database
and marking them as _p_changed.

Marius Gedminas
-- 
Whom the gods would destroy, they first teach BASIC.
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