Example CouchDB design document with map-reduce

design-doc.js

// Most of the times an aggregation function is needed,
// it is a simple count or sum, which are supported by
// built-in functions of both CouchDB and MongoDB.
//
// This is a CouchDB design document:

var circlesDesignDoc = {
  url: '_design/circles',
  body: {
    version: "1.0.1",
    language: "javascript",
    views: {
      count: {
        map: function (doc) {
          if (doc.type === "circle") {
            emit(null, doc._id);
          }
        },
        reduce: "_count"
      }
    }
  }
};