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From Jurg van Vliet <>
Subject Re: Howto drop rows with reduce?
Date Wed, 29 Apr 2009 18:34:37 GMT
hi luke,

thanks for your reply :)

i have comments for different types of documents, that is what makes  
it complicated. i have comments for files and comments for articles.  
if i map my documents of type Article and Comment to be reduced the  
way below i get all articles, and all comments. also the comments for  

the way i see how this could be implemented is to give the comment a  
type matching the type of its parent. the comment type would be  
ArticleComment. then something like the code we talk about would work.

working this through i start to understand map/reduce better and  
better. but i feel a different way of modeling is required to  
construct aggregated documents reflecting these relationships.

i guess we need to find a different way to store the information in  
our documents. the way we choose is to enable simple nested comments.  
(we wanted a view that returned the comments nested, or at least in  
order of presentation. we want couchdb to work for us, not the app.)

:) so, what paul and you suggest does not work. it would work  
perfectly fine in a database with every Comment related to an Article.  
but we also have Comments related to Files.


On Apr 29, 2009, at 7:43 PM, Luke Randall wrote:

> Jurg van Vliet wrote:
>> if i don't emit anything in the last emit statement i get comments  
>> for all of my document types. then case i end up with a list of  
>> articles and comments, both with a comment count.
> Hi Jurg
> From what I understand of your situation, I don't see why what Paul
> suggested wouldn't work. If you have the following as your map
> function
> function(doc) {
>    if( doc.type == 'Article') {
>        emit( doc._id, 0);
>    } else if( doc.type == 'Comment') {
>        emit( doc.path[0], 1);
>    }
> }
> when you reduce it* you will have a list of articles with a comment
> count. Note that you there is no requirement to call emit for each
> document. If you don't want a document to appear in a view then just
> don't call emit on it. Reduce isn't meant to be used as a filter,
> that's what map is for.
> * Remember to add :group => true to your couchrest view call, as Futon
> silently adds it, but it otherwise defaults to being false.
> Sorry, this is basically a rehash of what Paul said, but it seems that
> you possibly misunderstood his suggestion. Either that or I
> misunderstood your reply, which is also quite possible... :)
> - Luke
> PS Sorry if this message breaks threading; I wasn't subscribed to the
> list, so I had to copy and paste this.

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