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From: Paul Davis <paul.joseph.davis@gmail.com>
Date: Sun, 26 Sep 2010 20:16:19 -0400
Message-ID: <AANLkTi=L7GXm70G069=hB9knUEpxCK0Fs+q3=n-nEfd8@mail.gmail.com>
Subject: Re: Subselect Possible?
To: user@couchdb.apache.org
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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=3Dquery_key&limit=3D1
?group_level=3Dlength(query_key)&key=3Dquery_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 <reeder.29@gmail.com> wrote:
> I've searched the wiki and googled for "subselect" and "subquery", and no=
t 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" repr=
esenation. =A0For example, the item with path "QG" is a child of the item w=
ith path "Q" and a parent of the item with path "QGC".
>
> The trickiest query is, in English, "find all items with work less than z=
ero and whether they have any children with work less than zero". =A0The SQ=
L for this is
> SELECT item.*, EXISTS (SELECT work FROM item AS d WHERE d.path > item.pat=
h AND d.path <=3D item.path || '\ufffd' AND d.work < 0) AS undonePrereq, FR=
OM 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) {
> =A0if (doc.work < 0) {
> =A0 =A0var key =3D [];
> =A0 =A0var i;
> =A0 =A0for (i=3D0; i<doc._id.length; ++i)
> =A0 =A0 =A0key.push(doc._id.charCodeAt(i));
> =A0 =A0emit(key, doc.work);
> =A0}
> }
>
> and the reduce function
> function(keys, values, rereduce) {
> =A0var shortestKeyLength =3D Infinity;
> =A0for (var i=3D0; i<keys.length; ++i) {
> =A0 =A0if (keys[i][0].length < shortestKeyLength)
> =A0 =A0 =A0 =A0shortestKeyLength =3D keys[i][0].length;
> =A0}
>
> =A0return [keys.length, shortestKeyLength, keys[0][0].slice(0,shortestKey=
Length), values.length];
> }
>
> A query such as
> curl -X GET 'http://127.0.0.1:5984/tracker1/_design/trackerA/_view/undone=
ArrayNum?startkey=3D\[45,65,65\]&endkey=3D\[45,65,9999\]&group_level=3D2'
> will return the data necessary for items at the second level, but the des=
ired items could be at any level.
>
>
>
> Doug Reeder
> reeder.29@gmail.com
> http://reeder29.livejournal.com/
> https://twitter.com/reeder29
>
> https://twitter.com/hominidsoftware
> http://outlinetracker.com
>
>
>
>
>
>
>
>
>