[ZODB-Dev] I would like append an indexer with uuid key at root of my ZODB, how can I append an function to commit event to update this uuid catalog ?

[Jim Fulton]

On Tue, Jun 28, 2011 at 3:50 AM, Stéphane Klein <stephane at harobed.org> wrote:
> Hi,
>
>
> I use ZODB to record some Resources.
>
> All my Resources have an "uuid" field.

What is this? An integer? If so, how many bits? A string?

A common strategy is to use integers as ids.

> All work well but I would like append a BTree to ZODB root object to
> "index" uuid of all my resources.

I assume "append" is a euphemism for insert an item, as the root
object is a mapping object.

> I would like record to this BTree index only Resources commited to ZODB
> database.
>
> How can I connect a function to "commit" event ?

You don't want to connect to any sort of commit event. Simply update
your index as your application code adds, updates or removed objects.
The updates to the index will only be saved if the transaction is
committed.  They will be automatically discarded if the transaction is
aborted.

> In this function, how can I found all object modified ?
> How can I found all object removed to the database ?

This is up to your application and requires and an application-level
strategy.  A common technique is to generate modification and removal
events in your application and wire these up to the index via event
subscribers.

Also, note that objects are never explicitly removed from the
database. Objects are explicitly removed from application containers
and it is up to the application to decide if this is significant.

> Other question : are there already a package to perform this task ?

As others have pointed out, there are many. These are often called
"catalogs".  Note that these usually involved frameworks that address
multiple related concerns:

- Assignment of ids. Ids are used as compact representation of
  documents so they can be efficiently stored and looked in indexes.
  Typically, integers are used.

- Indexing, possibly including management of multiple indexes
  together.

  Note that these indexes are often, even in the simple cases, more
  complex than simple BTrees, although they typically use BTrees. For
  example, indexes typically use forward and reverse mappings to
  facilitate inindexing without having to store old document values.

- Events to signal when objects should be added, updated, or removed
  from the index(es).

Jim

--
Jim Fulton
http://www.linkedin.com/in/jimfulton