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From Alexander Thomas <herr.alexander.tho...@googlemail.com>
Subject Re: How can I resolve an external relation in embedded documents
Date Mon, 12 Jul 2010 10:58:59 GMT
Hello Mat,

thank you very much. That was helpful. Especially the include_docs=true. 

Regards,
Alex


Am 09.07.2010 um 13:33 schrieb Matt Goodall:

> On 9 July 2010 11:53, Alexander Thomas
> <herr.alexander.thomas@googlemail.com> wrote:
>> Hello everybody,
>> 
>> my name is Alexander Thomas. I'm a freelance web developer from Vienna, Austria.
>> 
>> After playing around with CouchDb a bit I finally decided to give it a try in a first
real life project. So in case my question is trivial, don't hesitate to RTFM me and give me
a (helpful) pointer.
>> 
>> I have a document type called 'story'. A story can have multiple sections as embedded
documents, stored in an array.
>> 
>> {
>>   "_id": "story_14c2f7f84c9701",
>>   "_rev": "4-abf15eac70a379c9a60b889c9e73357e",
>>   "type": "story",
>>   "title": "Untitled",
>>   "modified": "2010-07-03 20:27:35",
>>   "sections": [
>>       {
>>           "text": "test 1",
>>           "author_id": id_of_author
>>       },
>>       {
>>           "text": "test 2",
>>           "author_id": id_of_author
>>       }
>>   ]
>> }
>> 
>> Each section may have a different author so I store authors in different documents
to avoid duplicates.
>> 
>> 
>> Reading the available documentation I was able to connect the story itself to an
author but what I would like to have is a view, which collects one / all stories + the information
of the author for each embedded section.
> 
> 
> Hi,
> 
> CouchDB includes a simple document linking mechanism. You could write
> a view that emitted a row for the story, and a row for each section
> author with value {"_id": id_of_author}. Then use an include_docs=true
> option when querying the view to retrieve the story's doc and all
> associated author docs. The view might look something like (untested):
> 
>    function(doc) {
>      if (doc.type == 'story') {
>        emit([doc._id, 'story'], doc._rev);
>        var authors = {};
>        for each (var section in doc.sections) {
>          authors[section.author_id] = true;
>        }
>        for (var author in authors) {
>          emit([doc._id, 'author'], {"_id": author});
>        }
>      }
>    }
> 
> However, if you're fetching multiple stories at a time then it's quite
> likely that the same author will be retrieved multiple times for
> different stories. Also, include_docs=true is not free.
> 
> So, if that's not going to work for you then your options are:
> 
> 1. Include the interesting author attributes in each section.
> 2. Make two calls to CouchDB - the 1st calls fetches the story or
> stories you're interested in; the 2nd call fetches any authors that
> appear in the stories you found.
> 
> Personally, I'd probably just accept that I need to make two calls.
> 
> Hope that helps.
> 
> - Matt


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