Active Record acts_as_tree documentation note

One quick note about the counter_cache that the documentation doesn’t make clear…

The doc says:

counter_cache - keeps a count in a children_count column if set to true (default: false)

In reality, the counter_cache is looking for a column called pluralclassnamehere_count in your tree table. So, for example, if I have a nodes table, it might look something like this:

| id           | int(11)       |      | PRI |         |       |
| updated_on   | timestamp(14) | YES  |     | NULL    |       |
| created_on   | timestamp(14) | YES  |     | NULL    |       |
| parent_id    | varchar(32)   | YES  |     | NULL    |       |
| name         | varchar(100)  | YES  |     |         |       |
| nodes_count  | int(11)       | YES  |     | 0       |       |

with an AR definition like this:

class Node < ActiveRecord::Base
  acts_as_tree :order => “name”, :counter_cache => true
end

NOTE: In Active Record 1.9.1, they fixed a bug which now handles multi-word names correctly. For example, LineItem class in your model would have a counter_cache column of line_items_count.

My LazyWeb invocation is for someone to write an acts_as_tree implementation for Rails which is performant in fetching whole sections of the tree with a single query (ideally).