How to Have DB transaction

Assuming that you mean to define transactions that are executed according to the ACID principle, you could check out Doctrine, as Pagekit's ORM is just some kind of a wrapper for this in most cases

The Pagekit ORM is build on top of Doctrine DBAL. Thus, you can use transactions the same was as in DBAL. For reference on how to implement it in Pagekit, you can refer to the session implementation.