On his CodeUtopia blog Jani Hartikainen gives an inside look at a feature of Doctrine, nested sets.

The Doctrine library comes with a feature called nested set, which makes saving trees in a database easy. However, it's quite easy to accidentally cause a lot of extra unneeded queries if not being careful. Here are some pointers to keep in mind while working with the nested set, and some example queries to make understanding it easier.

He gives an example, showing how to get rows from the database - parent and child - and some optimization tips to keep things light. There's also some pros and cons included for doing it either way (the standard fetching or using the more optimized versions).

Ivan Iordanov has posted a method he's come up with to extend the existing Zend_Db_Table functionality (of the Zend Framework) to create NestedSet models for your app.

Last days I've been trying to customize Zend's Framework. My goal is to create simpler models. Currently I'm making some db models that handle stuff around wide used designs. Such design is the Nested Set model. It is an adjacent list realized in SQL as a tree. You can find a good introduction to nested sets at mysql developer zone.

He steps through the creation of some example database tables, his class and controller to hook into the Zend Framework application and this full code for his interface class to make the NestedSet models easy.