databases/ruby-dm-is-nested_set 1.2.0 NetBSD

DataMapper plugin allowing the creation of nested sets from data models. Provides all the same functionality as dm-is-tree, plus tons more! Read on.

== What is a nested set?

Nested set is a clever model for storing hierarchical data in a flat table. Instead of (only) storing the id of the parent on each node, a nested set puts all nodes in a clever structure (see Example below). That is what makes it possible to get the all of the descendants (not only immediate children), ancestors, or siblings, in one single query to the database.

The only downside to nested sets (compared to trees] is that the queries it takes to know these things, and to move nodes around in the tree are rather complex. That is what this plugin takes care of (+ lots of other neat stuff)!

Nested sets are a good choice for most kinds of ordered trees with more than two levels of nesting. Very good for menus, categories, and threaded posts.