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 paul.joseph.davis@gmail.com
 designates 209.85.210.176 as permitted sender)
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
        h=mime-version:in-reply-to:references:from:date:message-id:subject:to
         :content-type:content-transfer-encoding;
        b=k85GfVc5nhhDAQISecdaMzdVD2gOtUVO9RCBHvfb4PhHh3poZcgAgIzGMBliZLvW5l
         rP8LmDJOtvJKIMWCEbyd6NB/QIV1H7dZUwWRQhDY/nnjuCR6zahkc3sPB9G2XKqKz76x
         YPh4eks3Kv5h5kzdP4kQRhCmRhlRVeQsUl6FU=
MIME-Version: 1.0
In-Reply-To: <04C82F94-CF83-45D9-B599-47A8DD7C0501@gmail.com>
References: <04C82F94-CF83-45D9-B599-47A8DD7C0501@gmail.com>
From: Paul Davis <paul.joseph.davis@gmail.com>
Date: Thu, 10 Dec 2009 10:51:58 -0500
Message-ID: <e2111bbb0912100751r41e26b1cy74c1f901c687a949@mail.gmail.com>
Subject: Re: No safe way to query and not ever reduce a view.
To: user@couchdb.apache.org
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

On Thu, Dec 10, 2009 at 10:27 AM, Luke Sneeringer
<lukesneeringer@gmail.com> wrote:
> Greetings,
> So I'm in a situation here, and perhaps I'm missing something obvious.
>
> I have four views. They work fine. Two of them have reduce functions, and=
 two of them don't. On views with a reduce function, CouchDB sends reduced =
replies unless you specifically tell it not to. Anyway, in this particular =
instance, I want to query a view that may or may not have a reduce function=
, but I want the non-reduced results.
>
> This seems simple enough...just add ?reduce=3Dfalse. However, if you send=
 ?reduce=3Dfalse to a map-only view, you get an error from CouchDB. I also =
can find no way to ask if a view is a map-view or a map-reduce-view. In oth=
er words, if I have a view that may or may not have a reduce function, the =
only way I can see to get non-reduced results is to send a request with ?re=
duce=3Dfalse, catch the exception that's raised if it was a map-only view, =
and send the query again without ?reduce=3Dfalse.
>

I've never considered the scenario where the view was being accessed
without knowledge of what view it was. Which seems odd, but if its
popping up on the ML, then there's probably quite a few other people
trying it as well.

> This feels quite clunky to me and not at all relaxing. I understand the s=
trict error checking, but I suppose it seems there should either be a salie=
nt way to see which request form I should use, or there should be a request=
 form that works in both cases? If I don't want reduced results, after all,=
 it shouldn't matter if I have a reduce function.

Chris Anderson yelled at me about that as well. When I was writing
that parsing I was attempting to fix a very common problem where
people were trying to use a query parameter and then failing to figure
out why CouchDB wasn't working as expected. I don't remember the exact
parameter, but it was the equivalent of "reduce=3Dfalse" with no reduce
function, and then the ML and IRC got filled with questions of
"There's no difference between reduce=3Dfalse and not specifying it!
What's up with that?"

So after awhile I fixed it and now the URL processing tries to detect
as many errors as possible and complain loudly.

> Which brings me to the mailing list. Am I missing something? I looked in =
the manual, and found nothing. Is this in CouchDB? If so, how do I do it?
>

Nothing yet. Though as part of the ensuing discussion on whether this
exact scenario should be an error or not I made the suggestion that
maybe our views should use two URL handlers. Something like:

http://127.0.0.1:5984/db_name/_design/foo/_map/bar
http://127.0.0.1:5984/db_name/_design/foo/_reduce/bar

But I got yelled at for suggesting API changes.

HTH,
Paul Davis