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Date: Sun, 19 Jul 2009 22:17:18 -0700
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Subject: filter for _changes
From: Chris Anderson <jchris@apache.org>
To: dev@couchdb.apache.org
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Devs,

I've just committed a patch (r795687) that adds the ability to filter
_changes requests with a JavaScript function.

The function signature is:

function(doc, req, userCtx) {
  return (true or false);
}

When it returns true (or something truthy, like a non-empty string or
a non-zero number), the change is passed along to the user, otherwise
it is skipped.

The filter functions are stored on design documents under the
"filters" field. The current best source of documentation is the
changes.js test.

To query changes with a filter, the syntax is like:

GET /db/_changes?filter=ddocname/filtername

The biggest problem with this patch is that it uses a JavaScript OS
process per connected filtered listener. Fixing this is an
optimization as it won't effect the API, which is why I'm comfortable
committing this.

I'd appreciate some review to make sure the implementation is on the
right track.

Cheers,
Chris

-- 
Chris Anderson
http://jchrisa.net
http://couch.io