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From Nicolas Clairon <>
Subject Re: group_level and sorting
Date Mon, 20 Apr 2009 14:30:58 GMT
On Mon, Apr 20, 2009 at 3:39 PM, Wout Mertens <> wrote:
> On Apr 20, 2009, at 9:51 AM, Nicolas Clairon wrote:
>> = Reducing to get summary =
>> So, we have 3 documents A (with "title1" as title) but I want to
>> display only one to my users.
>> The displayed document will show the most releval informations (the
>> most use description) and
>> all the tags. So I created a reduce function wich summaries all the 3
>> documents into a single one :
>> reduced_documentA = {
>>  "title":"title1",
>>  "description":"a document A",
>>  "tags":["tag1","tag2","tag3"],
>>  "date_creation": 1
>> }
>> Note that the reduced document took the earlier date_creation.
> Hmmm... Remember that reduce results should not grow faster than log(n) for
> n documents. If everyone uses a different tag, that can become a problem. Of
> course, if you're not expecting thousands of tags, that shouldn't be a real
> issue.

I don't expect thousands of tags but it might be possible that each
document is so
different that I can have "nb_results_map" = "nb_results_reduce" (if,
for instance,
the description is different for each document).

How can I handle this issue ?

>> = Displaying the reduce document =
>> The challenge now, is to display the reduced document by tags then by
>> date_creation.
>> That's all.
>> How can I do that ? If I use a map function :
>>  emit([doc.tag[t], doc.date_creation], doc.title);
>> i will have duplication.
> So use
> emit([doc.tag[t], doc.date_creation, doc.title], null);
> No duplication.
>> I thought that I can user external process for that. Each time the
>> reduced_document
>> is updated, external process will store the reduced_document as
>> regular document in
>> another db (so that I can query it simplier).
> The problem is, knowing when the reduced_document is updated. You could get
> updates when a document is inserted and then query your reduced view, to see
> if the reduced document changed, and if so insert it in your database again.

I found a solution : process this by program. Each time user create a DocumentA,
I copy the reduced result into another database as a document (if the document
already exists, I'll updated it).

I could use update notifications but couchdb is not verbose enougth. I
can't get the id
of the updated document.


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