How can I get a view of favorite user documents by user in Couchdb map/reduce? - couchdb

Question

My Couchdb database as a main document type that looks something like:
{
"_id" : "doc1",
"type" : "main_doc",
"title" : "the first doc"
...
}
There is another type of document that stores user information. I want users to be able to tag documents as favorites. Different users can save the same or different documents as favorites. My idea was to introduce a favorite document to track this something like:
{
"_id" : "fav1",
"type" : "favorite",
"user_id" : "user1",
"doc_id" : "doc1"
}
It's easy enough to create a view with user_id as the key to get a list of their favorite doc IDs. E.g:
function(doc) {
if (doc.type == "favorite") {
emit(doc.user_id, doc.doc_id);
}
}
However I want to list of favorites to display the user_id, doc_id and title from the document. So output something like:
{ "key" : "user1", "value" : ["doc1", "the first doc"] }

Answer 1

In CouchDB 0.11 (just recently released), the include_docs=true feature allows you to look up any document in your view row. For example:
function(doc) {
if(doc.type == "favorite") {
emit(doc.user_id, {_id: doc.doc_id});
}
}
When you query your view with include_docs=true, you should see JSON like this:
// ... normal stuff
rows: [
{
"key":"user1",
"value":{"_id":"doc1"},
"doc": {
"_id" : "doc1",
"type" : "main_doc",
"title" : "the first doc"
// ...
}
},
{
// another doc, etc...
}
]

Answer 2

If you can't use the include_docs=true feature with v0.11, then you must have all information on-hand when you emit data for your view/map.
Instead of a traditional "join" style, consider storing a list of "favoriting" users in the main_doc documents.
{
"_id" : "doc1",
"type" : "main_doc",
"title" : "the first doc",
"favorited_by": ["user1", "user2"]
// ...
}
That way when your view runs, you can emit everything based on the information in that one document.
function(doc) {
if(doc.type == "main_doc") {
for (var a in doc.favorited_by) {
emit(doc.favorited_by[a], [doc._id, doc.title]);
}
}
}