There are some good guides out there explaining how to work with events and the ways to attach them to your components, but none (that I know) explain the following way to configure your events with CAction classes on your controllers the following way.
Uploading files in a webapp can be extremely tricky and sometimes the quickest way to do it is to store the file directly in the webserver or into a DNS (like Amazon S3) and then to save the link and the metadata inside a table in the DB. The thing is that you'll have to deal with file permissions, server storage, file management and so on (which is perfectly fine, by the way).
Lots of people are asking how to solve it with YII,We think its difficult with YII. But its easy to solve . There is no database triggers needed . we can simply sove it by extending a class(say "RActiveRecord") from CActiveRecord .Then extend all our model classes from that class.