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    <p><strong>Update</strong></p> <blockquote> <p>Note on JavaScript API change: Prior to Tue, 20 May 2008 (Subversion revision r658405) the function to emit a row to the map index, was named "map". It has now been changed to "emit".</p> </blockquote> <p>That's the reason why there is <code>map</code>used instead of <code>emit</code>it was renamed. Sorry I corrected my code to be valid in the recent version of CouchDB.</p> <p><strong>Edit</strong></p> <p>I think what you are looking for is a has-many relationship or a join in sql db language. Here is a <a href="http://www.cmlenz.net/archives/2007/10/couchdb-joins" rel="nofollow">blog</a> article by Christopher Lenz that describes exactly what your options are for this kind of scenario in CouchDB.</p> <p>In the last part there is a technique described that you can use for the list you want. You need a map function of the following format</p> <pre><code>function(doc) { if (doc.type == "text_file") { emit([doc._id, 0], doc); } else if (doc.type == "text_fragment") { emit([doc.file_id, 1], doc); } } </code></pre> <p>Now you can query the view in the following way: </p> <pre><code>my_view?startkey=["text_file_id"]&amp;endkey;=["text_file_id", 2] </code></pre> <p>This gives you a list of the form</p> <ul> <li>text_file</li> <li>text_fragement_1</li> <li>text_fragement_2</li> <li>..</li> </ul> <p><strong>Old Answer</strong></p> <p>Directly from the <a href="http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views#Reduce_Functions" rel="nofollow">CouchDB Wiki</a></p> <pre><code>function (key, values, rereduce) { return sum(values); } </code></pre> <p>Reduce functions are passed three arguments in the order key, values and rereduce</p> <p>Reduce functions must handle two cases:</p> <ol> <li><p><strong>When rereduce is false:</strong></p> <ul> <li>key will be an array whose elements are arrays of the form [key,id], where key is a key emitted by the map function and id is that of the document from which the key was generated.</li> <li>values will be an array of the values emitted for the respective elements in keys i.e. <code>reduce([ [key1,id1], [key2,id2], [key3,id3] ], [value1,value2,value3], false)</code></li> </ul></li> <li><p><strong>When rereduce is true:</strong></p> <ul> <li>key will be null</li> <li>values will be an array of values returned by previous calls to the reduce function i.e. <code>reduce(null, [intermediate1,intermediate2,intermediate3], true)</code> Reduce functions should return a single value, suitable for both the value field of the final view and as a member of the values array passed to the reduce function.</li> </ul></li> </ol>
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    1. POWhat is in the reduce function arguments in CouchDB?
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    1. POWhat is in the reduce function arguments in CouchDB?
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    1. COThanks, but I don't understand how to use that. I edited my first post with details about the problem I am trying to solve.
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    2. COI had already managed to get the result they get in the article, that is a list of (file, text_fragment) couples. But what I'd like is a list of (file, [text_fragment1, text_fragment2...]) where each file appears in only one couple, and the other coordinate of the couple contains all the text fragments corresponding to that file.
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    3. COMaybe I missed something since in the article they make a call to "map" instead of "emit". I have no idea where this "map" function comes from and what it does. I think I'm going to give up. I green check you as you completely answered the original question of the topic.
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Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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