/** Initialize an existing object from an associative array retrieved from the datbase.
	*
	* @param $assocArray Associative Array with the columnNames as keys and the values as values
	* @param $fieldMap Associative Array with the fieldNames as keys and the corresponding columnNames as values
	* @returns Associative Array mapping the fields that where not in $assocArray
	*/
	function &initFromData($assocArray, &$fieldMap) {
		$missingFieldsMap = array();
		reset($fieldMap);
        foreach ($fieldMap as $field => $column)
            if ( isSet( $assocArray[$column] ) ) {
                $this->$field = $assocArray[$column];
            } else {
                $missingFieldsMap[$field] = $column;
            }
		return $missingFieldsMap;
	}