Mailing-List: contact user-help@couchdb.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@couchdb.apache.org
Received-SPF: neutral (athena.apache.org: local policy)
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Apple Message framework v1084)
Subject: Re: Dealing with sealed docs
From: Jan Lehnardt <jan@apache.org>
In-Reply-To: <6084E307-7CFB-4BAD-A12C-063272628B95@vpro.nl>
Date: Wed, 20 Apr 2011 14:59:00 +0200
Content-Transfer-Encoding: quoted-printable
Message-Id: <95333123-2B25-4E26-8C8A-D502C88D96B3@apache.org>
References: <6084E307-7CFB-4BAD-A12C-063272628B95@vpro.nl>
To: user@couchdb.apache.org


On 20 Apr 2011, at 14:11, Nils Breunese wrote:

> Hello all,
>=20
> I recently upgraded to CouchDB 1.0.2 for development and found some of =
our view map functions broke. Apparently it's no longer possible to =
modify data a doc in a view function before emitting. I found "Documents =
are now sealed before being passed to map functions." in the changelog =
for 1.0.2.
>=20
> This is an example of a map function which no longer works under =
1.0.2:
>=20
> ----
> function(doc) {
>  if(doc.type =3D=3D=3D 'schedule') {
>    var events =3D doc.events;
>    if (events) {
>      events.forEach(function(event) {
>        var broadcasters =3D event.broadcasters;
>        if (broadcasters) {
>          broadcasters.forEach(function(broadcaster) {
>            if(broadcaster =3D=3D=3D 'VPRO') {
>              event.channel =3D doc.channel;
>              event.channelName =3D doc.channelName;
>              emit(event.end, event);
>            }
>          });
>        }
>      });
>    }
>  }
> }
> ----
>=20
> A colleague suggested using this:
>=20
> ----
> events.forEach(function(e) {
>  var event =3D eval(uneval(e));
> ----
>=20
> This creates a deep copy before modifying event properties. It works, =
but it looks ugly to me. Is this the way to go or is there a cleaner =
way?

I use JSON.parse(JSON.stringify(doc)) but that is essentially the same =
:)

The reason that doc modifications work were an artefact of a bug in =
Spidermonkey that finally got resolved. You shouldn't rely on being able =
to modify a doc in map functions.

That said, I'm surprised you get this error as you are not assigning =
anything do doc.events. Unless I got wrong how chaining in JS works, =
this shouldn't be a problem:

js> var a =3D {a:1};
js> seal(a);
js> a.a =3D 2;
typein:4: Error: a.a is read-only
js> var b =3D a.a;
js> print(b);
1
js> b =3D 2
2
js>=20

Cheers
Jan
--=20