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From J Chris Anderson <>
Subject Re: Chaining of views/MapReduce
Date Fri, 19 Feb 2010 15:10:23 GMT

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

> On 17.02.2010, at 23:15, Mario Scheliga wrote:
>> Hi Norman,
>> updating a document from map-function its not possible and seems to be the wrong
>> Thinking of map function processing docs seperatly (sandbox), so you are able to
>> spread the execution over thousand of servers ;-)
> 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. 

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=true and store the output into an empty db (one document per

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


> cheers,
> norman
>> greez
>> mario
>> Am 17.02.2010 um 21:04 schrieb Norman Rosner:
>>> Hi folks,
>>> 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.
>>> 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:
>>> 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
>>> 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)?
>>> Any help of you CouchDB kings would be greatly appreciated!
>>> Cheers,
>>> norman
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