code: function(connection, collection, options, cb) {
        return connections[connection].join(collection, options, cb);
      }
docs: Join
  
  Peforms a join between 2-3 orientdb collections when Waterline core
  needs to satisfy a `.populate()`.
  
  @param  {[type]}   connection  [description]
  @param  {[type]}   collection  [description]
  @param  {[type]}   options     [description]
  @param  {Function} cb          [description]
  @return {[type]}               [description]