code: public static function convertMultiField($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 != 'blob')
  		{
  			$objDatabase->query("ALTER TABLE `$table` CHANGE `$field` `$field` blob NULL");
  			$objDatabase->query("UPDATE `$table` SET `$field`=NULL WHERE `$field`=''");
  		}
  
  		while ($objRow->next())
  		{
  			$arrValues = StringUtil::deserialize($objRow->$field, true);
  
  			if (empty($arrValues))
  			{
  				continue;
  			}
  
  			$objHelper = static::generateHelperObject($arrValues);
  
  			// UUID already
  			if ($objHelper->isUuid)
  			{
  				continue;
  			}
  
  			foreach ($arrValues as $k=>$v)
  			{
  				// Numeric ID to UUID
  				if ($objHelper->isNumeric)
  				{
  					$objFile = FilesModel::findByPk($objHelper->value[$k]);
  					$arrValues[$k] = $objFile->uuid;
  				}
  
  				// Path to UUID
  				else
  				{
  					$objFile = FilesModel::findByPath($objHelper->value[$k]);
  					$arrValues[$k] = $objFile->uuid;
  				}
  			}
  
  			$objDatabase->prepare("UPDATE $table SET $field=? WHERE id=?")
  						->execute(serialize($arrValues), $objRow->id);
  		}
  	}
docs: Convert a multi source field to UUIDs
  
  @param string $table The table name
  @param string $field The field name