code: function(ref) {
              var keys = ref.split('.'),
                  key = keys.shift(),
                  result = _this.result[key];
  
              if(!result) {
                  // If the result does not exist, return an empty
                  throw new TypeError('Could not read property \'' + key + '\' from undefined');
              }
  
              // Iterate over all the keys and find the property
              while((key = keys.shift())) {
                  result = result[key];
              }
  
              if(_.isObject(result) && !_.isArray(result)) {
                  // Test if the result we have is an object. This means the user wants to reference
                  // to the _id of the object.
                  if(!result._id) {
                      // If no _id property exists, throw a TypeError that the property could not be found
                      throw new TypeError('Could not read property \'_id\' of ' + JSON.stringify(result));
                  }
  
                  return result._id;
              }
  
              return result;
          }
docs: This method searches for the _id associated with the object represented
  by the reference provided.
  
  @param  {String} ref The string representation of the reference.
  @return {String}     The reference to the object.