/** For polymorphic persistency a single peanut can be mapped to several tables.
	* This funtion returns a specific fiedMap for each table
	* Because a fields persistence can be PNT_READ_ONLY, the map for
	* loading the object is not necessarily the same as the map for saving.
	* This method returns the fieldmap for saving, this excludes fields whose 
	* propertyDescriptors' persistent === PNT_READ_ONLY
	* @param String $tableName the name of the table to get the map for
	* @return array fieldmap for saving, with fieldNames as keys and columnNames as values
	*/
	function getFieldMapForTable($tableName) {
		$fieldMap = array();
		$props = $this->getPersistentFieldPropertyDescriptors();
		if (empty($props))
			return $fieldMap;

		reset($props);
		foreach ($props as $name => $prop) {
			if (($prop->getTableName() == $tableName || $prop->getName() == 'id')
					&& ($prop->getPersistent() !== PNT_READ_ONLY))
				$fieldMap[$prop->getName()] = $prop->getColumnName();
		}
		return $fieldMap;
	}