In a tree-based model, you have some tradeoffs if you want to retrieve multiple values efficiently. Usually this is an insert-time vs query- time tradeoff. For example, if you wanted to keep track of the number of descendants of any particular node, you would either have to traverse the node's subtree to count all the children every time you wanted that information, or whenever you insert a child, you add one to the parent's descendant-count field, then the grandparent's, and so on, eventually bubbling this information up to the root. This way every node is guaranteed to have an up-to-date count.
Your situation is similar. You can add a descendants field containing an array of descendant IDs. Using the built-in activerecord serialization mechanism: class Person < ActiveRecord::Base serialize :descendants ... end Every time you create a new Person, all you need to do is descendants = new_person.parent.descendants descendants << new_person.parent.id Of course, this will be a bit more complex if you want to include dependants from multiple parents, but the idea is the same. Now every person includes a list of descendant IDs, and you'll need only a single query. -- Mark. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
