Passing an argument to map.js in a CouchApp view

I have a CouchApp that functions like a social network. I have a like button which, when clicked by a user, creates and saves a CouchDB JSON document with the fields post_id (the ID of the post that was liked), user_id (the ID of the user who liked the post), and type (value is "开发者_高级运维like," to indicate that the document is a like).

Alongside the post, I'd like to indicate the number of likes it has received. My map function looks like this:

function(doc) {
  if (doc.type && doc.type == 'like') {
    emit(doc.post_id, 1);
  }
}

and my reduce, this:

function(post_ids, likes) {
  return sum(likes);
}

My problem is, this function returns the sum of ALL the likes in ALL posts in the site. I'm thinking that my reduce.js is fine and that maybe I could tweak my map.js to accept a post_id argument so I can retrieve only the likes from that post_id, but how do I do that? The post_id comes from the design document, of course, when the "Like" button is clicked.

Thanks.

---

You need to look into the group view parameter. If you supply no querystring parameters, the default is to reduce the entire contents of the view. Once you apply group=true, you can also use key or startkey/endkey to pick out the post id(s) you need.

Also, there are built-in reduce functions that can perform basic reduce operations much more efficiently. (since they are compiled erlang code, not javascript source) Just put _count in place of your entire reduce.js. (You can even leave off the 1 in your emit)