On Mar 19, 2009, at 1:53 AM, Anand Chitipothu wrote:
I came across an earlier discussion on "behavior of document
revisions"[1], which says that:
A revision in CouchDB is meant to be used to test if a document has
changed since the last time you looked (useful for async updates
example) and not to actually look back in time at the document.
[1]: http://osdir.com/ml/db.couchdb.devel/2008-01/msg00123.html
Does it mean that if I want to create a wiki, I have to manage my own
document revisions? Like shown in this blog post[2]?
[2]: http://prematureoptimization.org/blog/archives/59
Yes. Note that you have some choice about where and how to store
history. You can store the full contents of old versions or just the
diffs that will get those; you can store the history in the document
or in separate documents.
I tried to extend the wiki idea in [2].
Here are my views assuming that every page has path, title, body and
revision.
{
"_id": "_design/wiki",
"language": "javascript",
"views": {
"page": {
"map": "function(doc) { emit([doc.path, doc.revision],
doc)}"
},
"by_title": {
"map": "function(doc) { emit(doc.title, doc)}",
"reduce": "function(key, values, rereduce) { var doc =
{'revision': 0}; for (var i in values) if (values[i].revision >
doc.revision) doc = values[i]; } return doc; }"
}
}
}
Actions:
* get latest version of a page:
/wiki/_design/wiki/_view/page?startkey=["foo",
"Z"]&descending=true&limit=1
Shouldn't that be /wiki/_design/wiki/_view/page?
endkey=["foo","Z"]&descending=true&limit=1 ? I didn't test this. BTW
hopefully we'll get open-ended searches before 0.9.0 lands which would
make this query prettier.
Is this is the right approach?
I think so although your database will grow large when you get a lot
of small changes to large pages.
I'm not quite happy with the above implementation of by_title as it is
indexing all the revisions, which is unnecessary.
If it doesn't index all revisions, how does it know which is the
latest one?
You could make the latest version of a document be the one with the
_id equal to the name. You'd have to store a copy or a diff before you
store changes to it though. Using that approach you wouldn't need the
by_title view.
Another approach: make _id be equal to "name<reserved char>version",
for example disallow the use of # in wiki names and store version 2 of
a page called foo as "foo#2". Then if you simply GET /wiki/_all_docs
(with view filters) you can get all revisions of a document, no views
needed. You'd get the latest version with the same limit=1 approach.
Wout.
