Mailing-List: contact user-help@couchdb.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@couchdb.apache.org
Received-SPF: pass (nike.apache.org: domain of simonmetson@googlemail.com
 designates 74.125.82.52 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=googlemail.com; s=gamma;
        h=message-id:from:to:in-reply-to:content-type
         :content-transfer-encoding:mime-version:subject:date:references
         :x-mailer;
        b=cyFNOv0mMY6zUUJ2vFKIMc2zpk6xhGVksjf8LGLVxxg5539v7wXwgLLGPu+I7hvIcW
         3rVlHzBuTa3Lio7A6Vh1OPlfD/ztd1WBnA87fvyW6DOfOIdOAtMaL1br8FcDDHrvtiuz
         RGy//lamoOdbAqkE2e4FAy6MqK0ee/jMFOaLQ=
Message-Id: <37323EC8-2A4A-474E-8E79-EA1DB540A441@googlemail.com>
From: Simon Metson <simonmetson@googlemail.com>
To: user@couchdb.apache.org
In-Reply-To: <z2tccadeb881004160146x3b54e990s2a78979c3a9a33dd@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed; delsp=yes
Content-Transfer-Encoding: quoted-printable
Mime-Version: 1.0 (Apple Message framework v936)
Subject: Re: getting most recent doc
Date: Sat, 17 Apr 2010 07:37:01 +0100
References: <l2jccadeb881004151533p1f97af17r6c82f460d4f42398@mail.gmail.com>
 <o2t46aeb24f1004151542y6fe2d765yd7d53de2231f4737@mail.gmail.com>
 <z2tccadeb881004160146x3b54e990s2a78979c3a9a33dd@mail.gmail.com>

Hi,
	If your timestamp is the time couchdb gets the document could =
you =20
possibly ditch the view and just use _changes?
Cheers
Simon

On 16 Apr 2010, at 09:46, wolfgang haefelinger wrote:

> Thanks Robert
>
> for your answer. However, it is not exactly what I was looking for
> (due to my inappropriate problem description).
>
> Firstly, I do want to have the document instead of the time stamp in
> order to avoid that additional document fetch. That's obviously easy
> to fix:
>
> function(doc) { //
> emit([doc.name, doc.timestamp], doc);
> }
>
> However, in my original attempt I can easily get an overview over all
> categories using "group=3Dtrue". And again my apologies for not having
> mentioned this - that's what I actually want:
> * I want to have an overview over all "categories" where each category
> is associated with the most recent event (document).
> * Another goal is to limit the traffic to a minimum, i.e. I don't want
> to discard or skip items returned by the (couchdb) server.
>
> Your map function works fine - if I know the category names in
> advance. Assume that I have N categories. Then I have to query the
> server N+1 times in order to present the overview (1 query to get all
> categories and N queries to get most recent event document).
>
> This is exactly the same as my second attempt: 1 query to get
> categories and most recent document id plus N simple get queries
> fetching documents. But what I was wondering is, whether I can avoid
> that extra N queries?
>
> // Regards
>
> P.S.:
> Obviously is your example more flexible as it would very easily allow
> me to calculate the most N recent events.
>
> P.P.S.:
> Btw, I had some hard times regarding parameter "descending" which is
> IMHO harmful documented ("reverse the output" =3D> no, not at all!) =
and
> inappropriate named. What "descending" does is changing the "key
> traversal order", not more and not less. The output of that traversal
> is unchanged.
>
>
>
>
>
> On Fri, Apr 16, 2010 at 12:42 AM, Robert Newson =
<robert.newson@gmail.com=20
> > wrote:
>> Something like;
>>
>> map;
>> function(doc) {
>>  emit([doc.name, doc.timestamp], null);
>> }
>>
>> no reduce method.
>>
>> with calls like;
>>
>> http://localhost:5984/db/_design/ddoc/_view/view?startkey=3D["name",=20=

>> {}]&endkey=3D["name"]&descending=3Dtrue&limit=3D1
>>
>> should get you the latest (highest timestamp) for document with
>> doc.name of "name"
>>
>> On Thu, Apr 15, 2010 at 11:33 PM, wolfgang haefelinger
>> <whaefelinger@gmail.com> wrote:
>>> My apologies for asking a probably rather stupid question ..
>>>
>>> Docs in my database are events. An event has a category name, a time
>>> stamp and lots of other details. I am looking for the most recent
>>> event.
>>>
>>> I started with something like
>>>
>>> function (doc) {              // map
>>>  emit(doc.name,doc)
>>> }
>>>
>>> function (ks,vs,rr) {
>>>  var maxdoc =3D max_timestamp(vs);
>>>  return maxdoc;
>>> }
>>>
>>> Although I'm reducing considerably, couchdb complains that I'm not
>>> reducing hard enough :-)
>>>
>>> (* Btw, what is actually the "reduce" limit? Do attachments count =20=

>>> as well?  *)
>>>
>>> Then I tried something like
>>>
>>> function (doc) {
>>>  emit(doc.name,{ "_id" : doc._id, "ts" : doc.timestamp});
>>> }
>>>
>>> and with a "virtually" unchanged reduce function. Now I'm below
>>> couchdb's reduction limit. However, this view does not return the =20=

>>> most
>>> recent document I was looking for but the "id" of that document.
>>>
>>> I had some hope that query parameter "include_docs=3Dtrue" would do =20=

>>> the
>>> magic (that's why I used "_id" as property name). But then I learned
>>> that "include_docs" is not supported for "reduced" views which =20
>>> took me
>>> by surprise. What could be the rational for this behaviour?
>>>
>>> In summary:
>>> * Is there a way to get the "most recent" document via a view?
>>>
>>> // Regards
>>>
>>
>
>
>
> --=20
> Wolfgang H=E4felinger
> h=E4felinger IT - Applied Software Architecture
> http://www.haefelinger.it
> +31 648 27 61 59