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From "Luke Burton (JIRA)" <>
Subject [jira] Commented: (COUCHDB-707) Proposal for "Filter Views"
Date Thu, 25 Mar 2010 20:23:27 GMT


Luke Burton commented on COUCHDB-707:

Hah, I picked a bad example. Forget attachments and images. In my case, I actually have rather
large hashes stored in documents. I chose images thinking it would better illustrate the point
of working with unwieldy documents. Sorry for the confusion! 

So in my case I don't have any affordances for using attachments, and I can't create a view
that emits the values that I want along with the lookup keys because what I need is the *entire*
document at the end (it populates records in a SproutCore frontend). 

As to what is "natural" with Couch: this is a database that can host its own apps! I don't
think I'm crossing any natural couch boundaries here :) Really this is just a small extension
to the idea of list views. In fact you could use the list view entirely for this if we just
added one JS call that effectively did: "emit these complete document IDs." But I think it's
different enough that it might merit its own place.

> Proposal for "Filter Views"
> ---------------------------
>                 Key: COUCHDB-707
>                 URL:
>             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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