Spot\Entity::isModified PHP Method

    public function isModified($field = null)
    {
        if (null !== $field) {
            if (array_key_exists($field, $this->_dataModified)) {
                if (is_null($this->_dataModified[$field]) || is_null($this->_data[$field])) {
                    // Use strict comparison for null values, non-strict otherwise
                    return $this->_dataModified[$field] !== $this->_data[$field];
                }
                return $this->_dataModified[$field] != $this->_data[$field];
            } elseif (array_key_exists($field, $this->_data)) {
                return false;
            } else {
                return null;
            }
        }
        /* Check if any of values really has changed. */
        foreach (array_keys($this->_dataModified) as $field) {
            if (true === $this->isModified($field)) {
                return true;
            }
        }
        return false;
    }