code: public static function convertSingleField($table, $field)
  	{
  		$objDatabase = Database::getInstance();
  
  		// Get the non-empty rows
  		$objRow = $objDatabase->query("SELECT id, $field FROM $table WHERE $field!=''");
  
  		// Check the column type
  		$objDesc = $objDatabase->query("DESC $table $field");
  
  		// Change the column type
  		if ($objDesc->Type != 'binary(16)')
  		{
  			$objDatabase->query("ALTER TABLE `$table` CHANGE `$field` `$field` binary(16) NULL");
  			$objDatabase->query("UPDATE `$table` SET `$field`=NULL WHERE `$field`='' OR `$field`=0");
  		}
  
  		while ($objRow->next())
  		{
  			$objHelper = static::generateHelperObject($objRow->$field);
  
  			// UUID already
  			if ($objHelper->isUuid)
  			{
  				continue;
  			}
  
  			// Numeric ID to UUID
  			if ($objHelper->isNumeric)
  			{
  				$objFile = FilesModel::findByPk($objHelper->value);
  
  				$objDatabase->prepare("UPDATE $table SET $field=? WHERE id=?")
  							->execute($objFile->uuid, $objRow->id);
  			}
  
  			// Path to UUID
  			else
  			{
  				$objFile = FilesModel::findByPath($objHelper->value);
  
  				$objDatabase->prepare("UPDATE $table SET $field=? WHERE id=?")
  							->execute($objFile->uuid, $objRow->id);
  			}
  		}
  	}
docs: Convert a single source field to UUIDs
  
  @param string $table The table name
  @param string $field The field name