Chris@909: module ActiveRecord
Chris@909:   module Acts
Chris@909:     module Tree
Chris@909:       def self.included(base)
Chris@909:         base.extend(ClassMethods)
Chris@909:       end
Chris@909: 
Chris@909:       # Specify this +acts_as+ extension if you want to model a tree structure by providing a parent association and a children
Chris@909:       # association. This requires that you have a foreign key column, which by default is called +parent_id+.
Chris@909:       #
Chris@909:       #   class Category < ActiveRecord::Base
Chris@909:       #     acts_as_tree :order => "name"
Chris@909:       #   end
Chris@909:       #
Chris@909:       #   Example:
Chris@909:       #   root
Chris@909:       #    \_ child1
Chris@909:       #         \_ subchild1
Chris@909:       #         \_ subchild2
Chris@909:       #
Chris@909:       #   root      = Category.create("name" => "root")
Chris@909:       #   child1    = root.children.create("name" => "child1")
Chris@909:       #   subchild1 = child1.children.create("name" => "subchild1")
Chris@909:       #
Chris@909:       #   root.parent   # => nil
Chris@909:       #   child1.parent # => root
Chris@909:       #   root.children # => [child1]
Chris@909:       #   root.children.first.children.first # => subchild1
Chris@909:       #
Chris@909:       # In addition to the parent and children associations, the following instance methods are added to the class
Chris@909:       # after calling <tt>acts_as_tree</tt>:
Chris@909:       # * <tt>siblings</tt> - Returns all the children of the parent, excluding the current node (<tt>[subchild2]</tt> when called on <tt>subchild1</tt>)
Chris@909:       # * <tt>self_and_siblings</tt> - Returns all the children of the parent, including the current node (<tt>[subchild1, subchild2]</tt> when called on <tt>subchild1</tt>)
Chris@909:       # * <tt>ancestors</tt> - Returns all the ancestors of the current node (<tt>[child1, root]</tt> when called on <tt>subchild2</tt>)
Chris@909:       # * <tt>root</tt> - Returns the root of the current node (<tt>root</tt> when called on <tt>subchild2</tt>)
Chris@909:       module ClassMethods
Chris@909:         # Configuration options are:
Chris@909:         #
Chris@909:         # * <tt>foreign_key</tt> - specifies the column name to use for tracking of the tree (default: +parent_id+)
Chris@909:         # * <tt>order</tt> - makes it possible to sort the children according to this SQL snippet.
Chris@909:         # * <tt>counter_cache</tt> - keeps a count in a +children_count+ column if set to +true+ (default: +false+).
Chris@909:         def acts_as_tree(options = {})
Chris@909:           configuration = { :foreign_key => "parent_id", :dependent => :destroy, :order => nil, :counter_cache => nil }
Chris@909:           configuration.update(options) if options.is_a?(Hash)
Chris@909: 
Chris@909:           belongs_to :parent, :class_name => name, :foreign_key => configuration[:foreign_key], :counter_cache => configuration[:counter_cache]
Chris@909:           has_many :children, :class_name => name, :foreign_key => configuration[:foreign_key], :order => configuration[:order], :dependent => configuration[:dependent]
Chris@909: 
Chris@909:           class_eval <<-EOV
Chris@909:             include ActiveRecord::Acts::Tree::InstanceMethods
Chris@909: 
Chris@909:             def self.roots
Chris@909:               find(:all, :conditions => "#{configuration[:foreign_key]} IS NULL", :order => #{configuration[:order].nil? ? "nil" : %Q{"#{configuration[:order]}"}})
Chris@909:             end
Chris@909: 
Chris@909:             def self.root
Chris@909:               find(:first, :conditions => "#{configuration[:foreign_key]} IS NULL", :order => #{configuration[:order].nil? ? "nil" : %Q{"#{configuration[:order]}"}})
Chris@909:             end
Chris@909:           EOV
Chris@909:         end
Chris@909:       end
Chris@909: 
Chris@909:       module InstanceMethods
Chris@909:         # Returns list of ancestors, starting from parent until root.
Chris@909:         #
Chris@909:         #   subchild1.ancestors # => [child1, root]
Chris@909:         def ancestors
Chris@909:           node, nodes = self, []
Chris@909:           nodes << node = node.parent while node.parent
Chris@909:           nodes
Chris@909:         end
Chris@909: 
Chris@909:         # Returns list of descendants.
Chris@909:         #
Chris@909:         #   root.descendants # => [child1, subchild1, subchild2]
Chris@909:         def descendants
Chris@909:           children + children.collect(&:children).flatten
Chris@909:         end
Chris@909: 
Chris@909:         # Returns list of descendants and a reference to the current node.
Chris@909:         #
Chris@909:         #   root.self_and_descendants # => [root, child1, subchild1, subchild2]
Chris@909:         def self_and_descendants
Chris@909:           [self] + descendants
Chris@909:         end
Chris@909: 
Chris@909:         # Returns the root node of the tree.
Chris@909:         def root
Chris@909:           node = self
Chris@909:           node = node.parent while node.parent
Chris@909:           node
Chris@909:         end
Chris@909: 
Chris@909:         # Returns all siblings of the current node.
Chris@909:         #
Chris@909:         #   subchild1.siblings # => [subchild2]
Chris@909:         def siblings
Chris@909:           self_and_siblings - [self]
Chris@909:         end
Chris@909: 
Chris@909:         # Returns all siblings and a reference to the current node.
Chris@909:         #
Chris@909:         #   subchild1.self_and_siblings # => [subchild1, subchild2]
Chris@909:         def self_and_siblings
Chris@909:           parent ? parent.children : self.class.roots
Chris@909:         end
Chris@909:       end
Chris@909:     end
Chris@909:   end
Chris@909: end