Hrm, I haven't thought this through to the end, but something that
might get you started:
Change your emit to emit(key, 1);
Change your reduce to:
function(keys, vals) {
return sum(vals);
}
Then query like such:
?key=query_key&limit=1
?group_level=length(query_key)&key=query_key
It seems like there should be a fancy way to get the reduce call to
tell you if the original node had < 0 work but I'm distracted by other
code right now.
HTH,
Paul Davis
On Sun, Sep 26, 2010 at 7:46 PM, Doug Reeder <[email protected]> wrote:
> I've searched the wiki and googled for "subselect" and "subquery", and not
> found anything relevelant.
>
> I'm evaluating whether CouchDB can handle an app which currently stores a
> tree structure in a relational database using the "materialized path"
> represenation. For example, the item with path "QG" is a child of the item
> with path "Q" and a parent of the item with path "QGC".
>
> The trickiest query is, in English, "find all items with work less than zero
> and whether they have any children with work less than zero". The SQL for
> this is
> SELECT item.*, EXISTS (SELECT work FROM item AS d WHERE d.path > item.path
> AND d.path <= item.path || '\ufffd' AND d.work < 0) AS undonePrereq, FROM
> item WHERE work < 0
>
> Can this be done in CouchDB, using a limited, small number of queries?
>
> My closest sally is the map function
> function(doc) {
> if (doc.work < 0) {
> var key = [];
> var i;
> for (i=0; i<doc._id.length; ++i)
> key.push(doc._id.charCodeAt(i));
> emit(key, doc.work);
> }
> }
>
> and the reduce function
> function(keys, values, rereduce) {
> var shortestKeyLength = Infinity;
> for (var i=0; i<keys.length; ++i) {
> if (keys[i][0].length < shortestKeyLength)
> shortestKeyLength = keys[i][0].length;
> }
>
> return [keys.length, shortestKeyLength,
> keys[0][0].slice(0,shortestKeyLength), values.length];
> }
>
> A query such as
> curl -X GET
> 'http://127.0.0.1:5984/tracker1/_design/trackerA/_view/undoneArrayNum?startkey=\[45,65,65\]&endkey=\[45,65,9999\]&group_level=2'
> will return the data necessary for items at the second level, but the desired
> items could be at any level.
>
>
>
> Doug Reeder
> [email protected]
> http://reeder29.livejournal.com/
> https://twitter.com/reeder29
>
> https://twitter.com/hominidsoftware
> http://outlinetracker.com
>
>
>
>
>
>
>
>
>
