Analytics - Join two collections in MongoDB

Analytics - Join two collections in MongoDB

/*
 * Pending - Covert _id to uid or vice versa
 */

// Collection 01 - users
users_map = function() {
  // Simply emit the msisdn and 0 for the file length.
  // The file length will come from the other collection.
  emit(this._id, { msisdn: this.msisdn, file_length: 0 });
}

// Collection 02 - files.files
files_files_map = function() {
  emit(this.uid, { file_length: this.length, msisdn: 0});
}

/*
 * Reduce function
 */
r = function(key, values) {
  var result = {file_length: 0, msisdn: 0};
  values.forEach(function(value) {
    // Sum up all the file_length from all for this UID (key)
    result.file_length += (value.file_length !== null) ? value.file_length : 0;
        
    // Only set msisdn once
    if (result.msisdn === 0 && value.msisdn !== null) {
      result.msisdn = value.msisdn;
    }
  });

  return result;
}

/*
 * Run mapReduce over both collections
 */
res = db.users.mapReduce(users_map, r, {out: {reduce: 'joined'}})
res = db.files.files.mapReduce(files_files_map, r, {out: {reduce: 'joined'}})