public function &orderBy($value)
    {
        if ($value === null || $value) {
            $this->order_by = $value;
        } else {
            throw new InvalidArgumentException('$value can be NULL or a valid order by value');
        }

        return $this;
    }
public function &orderBy($value)
    {
        if ($value === null || $value) {
            $this->order_by = $value;
        } else {
            throw new InvalidArgumentException('$value can be NULL or a valid order by value');
        }

        return $this;
    }
public function & orderBy ( $ value ) { if ( $ value === null || $ value ) { $ this -> order_by = $ value ; } else { throw new InvalidArgumentException ( '$value can be NULL or a valid order by value' ) ; } return $ this ; }
Set how system should order records in this collection.

@param  string $value
@return $this
Set how system should order records in this collection .