[Zope] ZCatalog Related Questions

[Kevin Dangoor]

----- Original Message -----
From: "James W. Howe" <jwh@allencreek.com>
To: <zope@zope.org>
Sent: Thursday, February 03, 2000 9:46 AM
Subject: [Zope] ZCatalog Related Questions


> One of the things I would like to do is have a full text search of all my
> articles.  However, it seems that the way I've structured things would
> require me to index all my DTMLMethods, whether they were contained in an
> article folder or not.  I can't seem to tell the system that I want to
> catalog only the DTMLMethods which are contained inside objects with a
> meta_type of 'Article', for example.  It seems that to get the behavior
> that I want I should store the article content in a property of my Article
> ZClass.  Then, I could just index that property value and I would only get
> data from that property.  What other ways are there to do this sort of
thing?

I'm currently doing it using a property, but the PrincipiaSearchSource
method that Evan mentioned should work out. The way you describe it in your
other message (making a PrincipiaSearchSource method that returns possible
massaged article_content) should work. One thing to note, though, is that
there was some discussion a while back about ZCatalog not calling DTML
methods in a completely useful way. I don't remember the final conclusion,
but I do know that I've had some trouble using a DTML method as an index.

Since your ZClasses are based on your own Python base classes, you can add
your own PrincipiaSearchSource in there, if you want. You can also add code
to automatically add/remove your items from the catalog. (Just look at
CatalogAwareness.py in the ZCatalog directory).

> Another question I have concerns the difference between Catalog Indexes
and
> Catalog Metadata.  From what I've read, it seems that items in Indexes are
> things you can specify in a search in order to find objects which have
> values corresponding to the index fields.  Metadata is information stored
> in the cataloged object itself and is immediately available rather than
> having to get the real object from the catalog object.  Is this
> correct?

Yes. This has the advantage of not activating the main object in the cache
(which is useful if you're searching lots of objects or large objects).

>  If I wanted to do a full text search, do I just define one index
> field with a value of TextIndex?  How does the TextIndex get populated.
If
> I define a TextIndex and do a find of all 'Articles', what will end up in
> the TextIndex?


Basically, you tell ZCatalog what name to look up for each object and to
index that in an TextIndex sort of index. So, if you specify
PrincipiaSearchSource as the thing to look up, the index will index all of
the words contained in or returned by PrincipiaSearchSource for all Articles
(since you specified that metatype).

As mentioned above, instead of doing a find you can also make your base
class act like CatalogAware (or even subclass CatalogAware if it does what
you want).

> Finally, is it generally true that a web site would define one ZCatalog
> (typically named 'Catalog') which contains data from all the different
> items that I might want to have cataloged?  For example, I have Article
> data that I'm interested in and I have Issue data that I'm interested
> in.  They don't have the same set of properties.  Do I just define one
> ZCatalog and define indexes for all of the properties that I'm interested
> in from both objects?

That's up to you. You can certainly do it that way. The properties that are
unique to Issues won't really cause a problem for Articles and vice versa.
To date, I've had all of my objects indexed in a single catalog. I'm
breaking some of them out now, however, because when you change something
that modifies the catalog from within a Version, that whole catalog is then
locked against changes. I have some things that only site administrators can
modify and other things that users can modify... so, if an administrator
makes a change in a Version, the whole site Catalog is locked, and the users
can't do their thing.

> I've read the information on ZCatalogs from zope.org but I still have
> questions.  Is there a place where I can see some additional examples of
> ZCatalog usage?

I haven't seen too many examples of using it. I'm sure you'll see it heavily
used in the Portal Toolkit.

Kevin