[Zope-dev] PathIndex doesn't index last part of path

[Casey Duncan]

A PathIndex is designed to make it more efficient to aggregate objects at
various levels of containment. Their primary use case AFAIK is to allow to
to limit queries to particular places within a hierarchy. The idea is to
eliminate recursive searching of leaf level folders when you want all
objects under a higher level and its child levels.

Also, by not indexing the nodes themselves, the index is an order of
magnitude smaller and searches are therefore faster and it takes less room
and is faster to update.

In fact there is no need to index the entire path of an object in the
catalog. Even with no Indexes defined, ZCatalog already does this for you.
The uid of every entry in the catalog is the full path to the object (as a
string). Unfortunately, ZCatalog does not expose this to the surface but you
can write a trivial external method to do it. And I might entertain adding a
ZCatalog API to do so if I had a good use case. Right now you can only
access entries by RID.

Now that begs the question, If you already know the path to the object you
are looking for, why are you using the Catalog in the first place? I highly
doubt doing what you describe below is faster than just directly accessing
the object. In fact I'd be willing to be its slower, especially since you
are searching two indexes to get it. Unless of course these are dynamically
generated objects of some kind (no stored in Zope).

As for making RIDs more permanent, that would basically require a rewrite of
the Catalog, and make certain operations much more expensive. As it stands,
your application should only assume that RIDs are valid within a single
transaction. You should use the path to uniquely identify objects, or some
application defined uid that gets cataloged otherwise.

-Casey

----- Original Message -----
From: "Andy McKay" <andy@agmweb.ca>
To: <zope-dev@zope.org>
Sent: Saturday, August 17, 2002 6:22 PM
Subject: [Zope-dev] PathIndex doesn't index last part of path


> This is mostly a question for AJ, but any input would be great. This bug
bit
> me today and is documented here:
> http://collector.zope.org/Zope/449/ISSUE_TRANSCRIPT/view
>
> I dont understand the brief argument against this one, it would make sense
> to me to able to pull an object out of the catalog based on its path. For
> example if I want /foo/bar/blammo, currently this means there is only one
> way of pulling the an object of the catalog given this path. Thats to send
> (path='/foo/bar', id='blammo'), rather than (path='/foo/bar/blammo'). Why
> wouldnt we want it this way?
>
> One thing I have done is store a whole bunch of references to objects as
> selected by the user. These are essentially random objects and the
quickest
> way is to pull them back out of the catalog. Of course I cant do more than
> one object per query (unless Im missing some other way) Id love to do
> (path=['/foo/bar/blammo', '/foo/bar/blammoz']) and get these 2 objects...
I
> think that would be neat.
>
> It would seem data_record_id_ is not guaranteed to permanent after a
> reindex_object (which CatalogAwareness uses), since this uncatalog and
then
> recatalogs the object. If this did work it would be cool and I could undo
> all the changes to my app back again.
>
> - The patch is already there, so Im curious why do we have what seems to
be
> a more limited design?
> - Would a halfway option such as path_match='final' be a choice that wont
> break any code but would confuse everyone and not make into the
> documentation?
> - Is it just a matter of fixing reindex_object as was suggested on #zope
so
> that data_record_id_ is more permanent?
>
> Cheers
> --
>   Andy McKay
>   Agmweb Consulting
>   http://www.agmweb.ca
>
>
>
>
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