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From mickael.bai...@free.fr
Subject Re: CouchDB The Definitive Guide - Part III
Date Tue, 07 Sep 2010 13:44:14 GMT
Hello,

CouchDB is basically a document store: you store documents in it, that are JSON objects (
see http://json.org/ ).
A document in CouchDB got 1 fundamental property : the key "_id" that is unique: two documents
can't have the same value for the "_id" property inside a couchdb database.
So Ok if you know the _id of a document you can get it back. But what if you don't know it
? What if you want to get all the documents on the database that have the property "foo" set
to "bar" ?
Enter the views. A view is a javascript function that YOU write, and that parses each document,
and sends back indexes (in couchdb we say the view emit indexes). See http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views
. Views are an implementation of the MapReduce algorithm used to compute data.
Now what if you want to change the output of the couchdb views, to get, say, HTML ? You use
lists. Lists take as input the view output (sort of), and you can format to your output of
choice (including HTTP headers, ...).
If you want to format a document to get it, in plain text, or in XML, or whatever you need,
instead of JSON, you use show functions. (see http://wiki.apache.org/couchdb/Formatting_with_Show_and_List
).

Views, lists, shows, and more (see http://wiki.apache.org/couchdb/Reference ) are stored in
special documents called design documents or ddocs, and that have "magic properties". For
example, a view will be stored in a design doc in the "views" property. CouchDB knows that
the "views" property of a design document is a special property containing code it should
run. Design documents are easily identified because their _id begins with "_design/". For
example : "_design/myWonderfulApp".

Now that you got :
- a server that can store data, create indexes to retrieve data the way it should for your
application, and even re-format data
- a client (the web browser) that can talk to the server (via ajax, websockets) and build
rich interfaces ( javascript once again)

you perhaps need a way to easily :
- store server functions (views, lists, shows...) that you edit in your favorite code editor
and store as text files
- store "client files" (html files, images, client-side javascript like jquery and sammy)
That's what couchapp provides.

Hope that helps

Regards,

Mickael

----- Mail Original -----
De: "Ido Ran" <ido.ran@gmail.com>
À: user@couchdb.apache.org
Envoyé: Mardi 7 Septembre 2010 11h51:27 GMT +01:00 Amsterdam / Berlin / Berne / Rome / Stockholm
/ Vienne
Objet: Re: CouchDB The Definitive Guide - Part III

Hi,

Thank you very much for sharing that.
I actually got to CouchDB through reading about MongoDB.
I mostly do desktop application using C# in the client side and J2EE on the
server side.
I did some ASP and ASP.NET applications in the past, never ruby though.

I see eye to eye with you about CouchApp are design documents, but there is
something more - there is the ability to run server side code "inside"
CouchDB.
The ability to have both Application server and Database server as the same
platform is what look interesting to me.
It for sure does not fit any application out there, but there are many
application that can benefit from this architecture.

I have a pretty simple application I'm trying to build (both to have it and
to learn CouchDB). The application is like a "gateway" to PicasaWeb albums.
It will have hierarchical directory like structure to organize the albums
(something not available in PicasaWeb) and will later just redirect you to
PicasaWeb for album view.
It should be "pure web" application, not activeX, flash, silverlight, just
HTML, JavaScript, CSS.
I try to use SproutCore for that but there is always the question of "where
to store the data". It is nice that SproutCore is server agnostic, but
eventually I need to put the data somewhere.
CouchDB look like better fit because it has both backend database as well as
web serving abilities.
BTW, I saw there are efforts to "merge" SproutCore and CouchDB. I think if
I'll be able to publish SproutCore application the same was I publish
CouchApp it will be one great piece of platform.

Thank you again and keep it up :)

Ido

On Tue, Sep 7, 2010 at 11:15 AM, Nicholas Orr <nicholas.orr@zxgen.net>wrote:

> Hi Ido,
>
> I thought I'd share how I got to know CouchDB.
> I heard about it via ruby channels and then read about couchapp however
> that
> had something to do with python and so went back to ruby.
> At the time (and now) couchrest was how I interacted with couch using futon
> to figure out views.
>
> Then I looked through the book again the other day and from what I gathered
> a couchapp built site is really just a design doc (which I also have not
> totally comprehended what these can do) and couchapp is no more than a
> bunch
> of script(s) to organise the design doc and is not required to actually
> run/render the site. If this line of thought is accurate one could use
> futon
> to build an app in it's entirety which is actually pretty cool.
>
> In my limited experience as long as you get documents, map/reduce your
> pretty much there and able to achieve a lot :)
>
> For now I really like using ruby (mainly cause I can write html and css in
> haml/sass) and will most likely be building apps that require the 3 layers
>
> Nicholas
>
> On Tue, Sep 7, 2010 at 5:39 PM, Ido Ran <ido.ran@gmail.com> wrote:
>
> > Hi,
> >
> > I have successfully download Pages from git and push it to my
> > couchone.comserver.
> > The application is working, but...
> >
> > It is still hard for me to understand how to change it and write my own
> > application.
> >
> >
> >   1. I don't understand what the ddoc is, but it looks important.
> >   2. I understand from the book the separation between documents, views,
> >   lists but still not enough to use them.
> >   3. When I push the CouchApp using Push command to my database
> everything
> >   get upload to a single document, is that supposed to be like that? All
> > the
> >   attachments are "jam" in single document in the database. It does not
> > look
> >   right for me, but I'm the new guy so :)
> >   4. I know it take time to learn stuff, but I have hard time find an
> >   anchor to hold to and get to the rest (if you see what I mean).
> >
> > As I said, I'll keep on trying. I spent about hour each night to progress
> > so
> > it's not very fast.
> >
> > Ido
> >
> >
> > On Mon, Sep 6, 2010 at 10:21 PM, J Chris Anderson <jchris@apache.org>
> > wrote:
> >
> > >
> > > On Sep 6, 2010, at 12:15 PM, Ido Ran wrote:
> > >
> > > > Thank you very much.
> > > > I'll try to use Pages and see how it goes.
> > > >
> > > > Does the draft version of the book is the "most recent" or is it the
> > > other
> > > > way around?
> > > >
> > >
> > > The draft is newer (and you are welcome to change it using Github)
> > >
> > > let us know how Pages goes!
> > >
> > > Chris
> > >
> > > > Thank you,
> > > > Ido
> > > >
> > > > On Mon, Sep 6, 2010 at 6:14 PM, J Chris Anderson <jchris@apache.org>
> > > wrote:
> > > >
> > > >>
> > > >> On Sep 5, 2010, at 11:37 PM, Ido Ran wrote:
> > > >>
> > > >>> Hi,
> > > >>> I'm learning CouchDB using the CouchDB Definitive Guide (draft
> > > edition).
> > > >>> I've got to part III where I start playing with Sofa application
to
> > get
> > > >> my
> > > >>> hand on real CouchApp, but there are some prolems:
> > > >>>
> > > >>>
> > > >>>  1. The code presented in the book does not match the code in
sofa
> > > >> github
> > > >>>  repository - jchris's sofa at master - GitHub<
> > > >> http://github.com/jchris/sofa>
> > > >>>  2. The application in the github repository does not work right.
I
> > can
> > > >>>  push it to CouchDB (I'm using couchone.com or couch.io server)
> but
> > > the
> > > >>>  post form does not work, currently because app.docForm is
> deprecated
> > > >> but I
> > > >>>  don't understand how to fix it.
> > > >>>  3. When I push the app to CouchDB server I get a database with
> > single
> > > >>>  document with _id of sofa. I thought it should be a collection
of
> > > >> documents,
> > > >>>  not single document.
> > > >>
> > > >> Thanks - these are serious issues... I've got a running copy of Sofa
> > at
> > > >> http://jchrisa.net so I know it can work. I've got to set aside a
> few
> > > days
> > > >> to test the book's instructions etc, make sure they still map to
> > > reality.
> > > >>
> > > >> In the meantime you can try running the Pages application (a wiki
> > which
> > > >> uses many of the same techniques as Sofa, but with a fresher
> > > implementation)
> > > >>
> > > >> http://github.com/couchone/pages
> > > >>
> > > >> The README to Pages is up to date and accurate.
> > > >>
> > > >> Best,
> > > >> Chris
> > > >>
> > > >>
> > > >>>
> > > >>> Thank you,
> > > >>> Ido
> > > >>
> > > >>
> > >
> > >
> >
>

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