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From "Luke Burton (JIRA)" <j...@apache.org>
Subject [jira] Created: (COUCHDB-707) Proposal for "Filter Views"
Date Wed, 24 Mar 2010 06:41:27 GMT
Proposal for "Filter Views"
---------------------------

                 Key: COUCHDB-707
                 URL: https://issues.apache.org/jira/browse/COUCHDB-707
             Project: CouchDB
          Issue Type: New Feature
          Components: JavaScript View Server
    Affects Versions: 0.11
            Reporter: Luke Burton


A common operation I find myself performing repeatedly is:

* request a view (maybe with some basic filter like "keys" or a range of keys)
* in my client, filter this view based on some complex criteria, leaving me with a small set
of document IDs (complex as in array intersections, compound boolean operations, & other
stuff not possible in the HTTP view API)
* go back to Couch and fetch the complete documents for these IDs.

List Views almost get me to the point of doing this purely in Couch. I can enumerate over
a view and do some complex things with it. But I can't output entire documents, unless I use
the include_docs=true flag which murders the performance of the list view.Apparently because
the entire view is fetched with including docs, THEN passed on to the list view JS. Typically
my complex filter criteria is contained in the view itself, so there is no need to fetch the
entire document until I know I have a match.

In summary, a Filter View would execute some arbitrary JavaScript on each view row, with access
to HTTP request parameters, and return "true" for rows that match. The output would be a list
of IDs for whom the function returned true. include_docs=true would include the matching documents.

Performance would certainly not be as good as fetching a raw view, but it would indisputably
be better than fetching the entire view over HTTP to a client, deserializing the JSON, doing
some stuff, then making another HTTP request, and deserializing more JSON.

I looked at the various entry points for list views in the Couch source. Unfortunately it
will take me some time to come up to speed with the source (if I ever have the time ...),
and I hope that what I'm asking for could be a simple extension to the List Views for someone
very familiar with this area.


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