On Nov 13, 2008, at 1:10 PM, ara.t.howard wrote:
On Nov 13, 2008, at 10:39 AM, Damien Katz wrote:
My answer is "Don't do that". Values in documents shouldn't depend
on values in other documents, that's a better fit for a relational
or OO DB. In your example though, CouchDB's views could be used to
compute the sums.
i don't think that's realistic. consider something like the
following:
let's say we write a publishing system, users can create documents
with content and tags. at the end of the month the editor is going
to write a summary of the content from that month, obviously this
summary should be tagged with the union of the tags from all
summarized content - for later searching. regardless of whether we
store the tags inside the document or outside of it we have quite a
task - we need to get a consistent read of all content for the
month, with all it's tags, in order to properly construct the
summary document with it's aggregate tags. this isn't strict
dependence - it's merely a read/write consistency issue which nearly
any application is going to face. we can argue that it's not
important that the summary of tags exactly mirrors the tags of it's
constituent parts, but that kind of thinking results not in an
information store, but a collection of valueless data.
CouchDB views are a consistent snapshot of the database, your reports
are generated from the views. The view APIs are the place to look for
better reporting capabilties.
anyhow, i think it's important to be able to agree upon best
practices for this kind of operation. saying that values shouldn't
depend on values in other documents is quite a statement - it means
couch should no be used for any information store where the
information value needs to grow recursively.
What I mean is you should never depend on the accuracy of the computed
values in documents that are based on other documents. Particularly
with replication.
in my case we're modeling financial information which gets processed
in increasingly sophisticated ways - where documents are inputs to
processes which produce other documents. i can't think of an
application that does not do the same thing: a blog comment depends
on the blog post, a 'friends list' depends on the users, etc.
are you referring to 'values' as different from 'ids' ?
Yes, I mean values as computed values. The main post shouldn't be
updated with a comment count or anything computed like that. It's fine
if comments have a reference to their parent, and its fine if the
comments are tagged as children of the post. This way, when the main
post is opened, the comment count can be computed from a view, or when
viewing a comment, the user is also shown the parent, and maybe
subcomments if its a threaded discussion.
-Damien
kind regards.
a @ http://codeforpeople.com/
--
we can deny everything, except that we have the possibility of being
better. simply reflect on that.
h.h. the 14th dalai lama
