[Zope] A Quick Event-based Cataloging How-to for Zope 2

[Chris Withers]

Hi All,

Just been playing with this and found it remarkably easy, so thought I'd 
pass it on. If anyone can think of a better place than the mailing list 
archives for this, please let me know!

Anyway, so I'm building a Zope 2 app where I need to index objects that 
are not catalog aware when they're added, modified or removed. To make 
things harder, this also needs to work via WebDAV.

OK, so here's the solution:

1. Create yourself a python module called subscribers.py and put it on 
your python path, containing the following:

from Acquisition import aq_base
from zope.interface import Interface

class ICatalogAware(Interface): pass

def catalog(object,event):
     if aq_base(object) is object:
         # ObjectModified can get emitted during creation,
         # before the object has any acquisition context
         return
     object.getPhysicalRoot().unrestrictedTraverse(
         '/catalog'
     ).catalog_object(object)

def uncatalog(object,event):
     object.getPhysicalRoot().unrestrictedTraverse(
         '/catalog'
     ).uncatalog_object('/'.join(object.getPhysicalPath()))

2. Slap the ICatalogAware marker interface on any classes you want to 
have indexed. Here's an example for the good old File object. Put the 
following in your site.zcml:

<class class="OFS.Image.File">
<implements interface="subscribers.ICatalogAware"/>
</class>

3. Finally, wire up the events so that files get indexed when they're 
created, modified or removed, again by adding the following to site.zcml:

   <subscriber
       handler="subscribers.catalog"
       for="ICatalogAware
            zope.app.container.contained.ObjectAddedEvent"
       />

   <subscriber
       handler="subscribers.catalog"
       for="ICatalogAware
            zope.app.container.contained.ObjectModifiedEvent"
       />

   <subscriber
       handler="subscribers.uncatalog"
       for="ICatalogAware
            zope.app.container.contained.ObjectRemovedEvent"
       />

4. Okay, sadly you do need to get do some patching if you want changes 
to the file to result in recataloging :-/ Here's a diff:

--- Image.py.original   2006-09-26 16:32:20.759375000 +0100
+++ Image.py    2006-09-26 16:33:11.384375000 +0100
@@ -33,6 +33,8 @@
  from ZPublisher.HTTPRequest import FileUpload
  from ZPublisher.Iterators import filestream_iterator
  from zExceptions import Redirect
+from zope.event import notify
+from zope.app.container.contained import ObjectModifiedEvent
  from cgi import escape
  import transaction

@@ -437,6 +439,7 @@
          self.ZCacheable_invalidate()
          self.ZCacheable_set(None)
          self.http__refreshEtag()
+        notify(ObjectModifiedEvent(self))

      def manage_edit(self, title, content_type, precondition='',
                      filedata=None, REQUEST=None):

Okay, well, hope this helps someone :-)

Chris

-- 
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            - http://www.simplistix.co.uk