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Date: Thu, 10 Jun 2010 16:33:41 +0300
Message-ID: <AANLkTikH8F8TxQfjmyNs1O2kiR3GQk7acGmLDoOgTOgp@mail.gmail.com>
Subject: Re: Calculating the sum of attachment sizes
From: Elf <elf2001@gmail.com>
To: user@couchdb.apache.org
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You may emit some of your group definitions as keys and size as value.
Like
view:

fun(doc) {
// attachments size calculations
emit([doc.user, doc.folder], attachments_size)
}

then, reduce will be like
fun(keys, values) {
return sum(values);
}

And then, you may query view with argument group =3D true and
group_level =3D 1 for calculate user-level space usage, or group_level =3D
2 for folder-level space usage.


2010/6/10 Moritz Post <moritzpost@gmail.com>:
> Hi CouchDB
>
> I want to calculate the sum of all attachments of a particular subset of
> documents. Here is my approach:
>
> =3D=3D Map =3D=3D
>
> function(doc) {
> =A0var localSum =3D 0;
> =A0for ( var i in doc._attachments) {
> =A0 =A0localSum +=3D doc._attachments[i].length
> =A0}
> =A0emit(doc._id, localSum);
> }
>
> =3D=3D Reduce =3D=3D
>
> function(key, values) {
> =A0return sum(values)
> }
>
> This works fine when i run this code from within futon without providing =
any
> subset of docs. It returns a single result { null,
> <totalSumOfAllAttachments>}
>
> But what i do in practice is using a POST on the view to provide the ids =
of
> documents of which totalsum i am interested in (eg 2 docs here):
>
> curl -d
> '{"keys":["a813cded7cfa807c6c48ae1d84004d45","a813cded7cfa807c6c48ae1d840=
01823"]}'
> -X POST
> http://localhost:5984/mydb/_design/mydesign/_view/getAttachmentSize?group=
=3Dtrue
>
> Here is the problem: I have to use group=3Dtrue when calling the view wit=
h
> POST parameters because it is a multi-key fetch (otherwise the couch
> complains). In this results i get a separate result entry for each docume=
nt
> since the grouping keys are obviously different for each doc._id. So i ge=
t
> something like:
>
> "a813cded7cfa807c6c48ae1d84004d45", 68346
> "a813cded7cfa807c6c48ae1d84001823", 23755
>
> but not the aggregated sum.
>
> I have to use the doc._id in the emit function though because otherwise t=
he
> filtering via the POST parameter would not limit the sum to the document
> subset i specified.
>
> So i hope one understands the problem and is able to point me in the righ=
t
> direction.
>
> If their is any better way to calculate the sum of all attachments sizes =
for
> a subset of documents i would also be very interested.
>
> Thanks in advance
> Moritz Post
>


--=20
----------------
Best regards
Elf
mailto:elf2001@gmail.com