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Subject: Re: Chaining of views/MapReduce
From: J Chris Anderson <jchris@couch.io>
In-Reply-To: <6B5D22A9-F9E5-4EEC-91B8-536A2BB571EF@googlemail.com>
Date: Fri, 19 Feb 2010 10:10:23 -0500
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To: user@couchdb.apache.org


On Feb 17, 2010, at 5:29 PM, Norman Rosner wrote:

>=20
> On 17.02.2010, at 23:15, Mario Scheliga wrote:
>=20
>> Hi Norman,
>>=20
>> updating a document from map-function its not possible and seems to =
be the wrong way.
>> Thinking of map function processing docs seperatly (sandbox), so you =
are able to
>> spread the execution over thousand of servers ;-)
>=20
> True that! But: suppose I'm just creating/updating one document per =
couchdb-instance, that should be ok, right? Because after that, I can =
easily get all the result documents and merge them together. I would do =
it in as similar way in Hadoop. And as far as I read in the loooong =
archives of this list, I'm not the only one who wants to do such things.=20=


The "proper" way to do this is to have a simple CouchDB map reduce view =
that is the 1st phase of your chain.

Then query the view with group=3Dtrue and store the output into an empty =
db (one document per row).

Now you can write another view on top of the derived db to do the second =
phase (sort by value, etc).

Chris

>=20
> cheers,
> norman
>=20
>>=20
>> greez
>> mario
>>=20
>> Am 17.02.2010 um 21:04 schrieb Norman Rosner:
>>=20
>>> Hi folks,
>>>=20
>>> first, I'll have to admit that I'm kinda new to JavaScript and of =
course to CouchDB.  Second I just reuse the subject so I hope it also =
pops up if anybody searches for it.
>>>=20
>>> As I read chaining of views is not possible yet but it's mentioned =
couple of times on the mailing list. So here's what I want to do:
>>>=20
>>> 1. Create a list of unique labels/tags/whatever through all of the =
documents (e.g. all nouns that are in the documents)
>>> 2. Extract all labels/tags/nouns of each document and check them =
again the before calculated result in some kind of way
>>>=20
>>> For the second point I created a view which works except of the =
checking against the result from point 1. Now I'm trying to solve point =
1.
>>> And here my questions begin: How can I create/update a document from =
inside of a map function? As I think of it, I'll have to make a HTTP GET =
to load the document in each iteration. I found some HTTP stuff in the =
test.js in the test folder, but I'm not quite sure how to use it and if =
it's the right way of thinking? Is there any way of using global =
variables throughout 'couchapps' (e.g. through the lib folder and =
thelike)?
>>>=20
>>> Any help of you CouchDB kings would be greatly appreciated!
>>>=20
>>> Cheers,
>>>=20
>>> norman
>>=20
>>=20
>> --
>> Sourcegarden GmbH HR: B-104357
>> Steuernummer: 37/167/21214 USt-ID: DE814784953
>> Geschaeftsfuehrer: Mario Scheliga, Rene Otto
>> Bank: Deutsche Bank, BLZ: 10070024, KTO: 0810929
>> Schoenhauser Allee 51, 10437 Berlin
>>=20
>=20