Mailing-List: contact user-help@couchdb.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@couchdb.apache.org
Received-SPF: pass (athena.apache.org: domain of jens@couchbase.com designates
 206.225.164.32 as permitted sender)
From: Jens Alfke <jens@couchbase.com>
To: "user@couchdb.apache.org" <user@couchdb.apache.org>
Date: Mon, 5 Nov 2012 14:31:00 -0800
Subject: Re: Exist test?
Thread-Topic: Exist test?
Thread-Index: Ac27pTszROxi+t5QStWCEO58tub3Zg==
Message-ID: <28887DC7-1DBE-42F9-82B3-18F28B393CCF@couchbase.com>
References: <99EA19FD-5ED6-4EDA-B538-2D78DCE47DFF@charter.net>
 <9D607BF7-197D-47C0-BCF8-3D225405C6CE@couchbase.com>
 <95FDB8AF-32C2-4056-9D3B-9FC05186F16C@charter.net>
 <CABvT1DEUjstEt8Szev5zbsz=3cdprr3m8bnFsO6D2B7eMwbB5A@mail.gmail.com>
 <3F2385CF-51CD-4A6F-BB41-DE730655BBCF@charter.net>
 <D1C809D1-AA41-4817-8B3C-646DC5E61FBE@couchbase.com>
 <FAB40052-323D-4D7A-A592-C43F8CFAA711@charter.net>
In-Reply-To: <FAB40052-323D-4D7A-A592-C43F8CFAA711@charter.net>
Accept-Language: en-US
Content-Language: en-US
acceptlanguage: en-US
Content-Type: text/plain; charset="Windows-1252"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0


On Nov 5, 2012, at 12:17 PM, Kevin Burton <rkevinburton@charter.net> wrote:

> When I create a new document both the id and rev will be null. So in orde=
r to determine if the create is a duplicate another field must be involved.

Gotcha. In general, if you have an attribute of a document that must be uni=
que within the database, it=92s a good idea to use that attribute (or a tra=
nsformed/canonicalized version of it) as the document ID. That way the data=
base itself can enforce the uniqueness. Otherwise you can end up in situati=
ons where there are multiple documents with that same attribute value, if y=
our app supports multiple clients or does replication.

> For example say my document had a field 'title' I could construct a view =
to return all documents that have a given 'title'. The reason that I brough=
t this up in this context is that if I could check to see if there were any=
 documents that had a particular title then I would be closer to finding ou=
t if the document had already been inserted in the db.

That=92s very easy to do. In generic CouchDB terms (I don=92t know DreamSea=
t or .NET), you would
* Create a design document containing a view with a map function:
	function(doc) {if (doc.title) emit(doc.title, null);}
* Query the view for a particular title by setting the startkey and endkey =
parameters to the title. You=92ll get back a list of the document(s), if an=
y, with that title.
* If you get back zero rows from the query, create a new document.

=97Jens=