CodeIgniter transaction, starting it and canceling it in different functions

[eluser]WebMada[/eluser]
Hi

I want to emulate draft in my backoffice forms: in fact, there are 2 buttons in my forms, "Overview" and "Save". Overview does not commit changes but it serves for displaying draft of the website.

Is it possible to start the transaction in Overview button.
And commit with Save button.
Cancel transaction (lose modification) when opening form.

How to do: never commit if Save button not clicked?

For my curiosity, what is the difference between trans_begin() and trans_start()??

Webmada