module ActsAsTree::ClassMethods

Specify this acts_as extension if you want to model a tree structure by providing a parent association and a children association. This requires that you have a foreign key column, which by default is called parent_id.

class Category < ActiveRecord::Base
  include ActsAsTree

  acts_as_tree :order => "name"
end

Example:
root
 \_ child1
      \_ subchild1
      \_ subchild2

root      = Category.create("name" => "root")
child1    = root.children.create("name" => "child1")
subchild1 = child1.children.create("name" => "subchild1")

root.parent   # => nil
child1.parent # => root
root.children # => [child1]
root.children.first.children.first # => subchild1

In addition to the parent and children associations, the following instance methods are added to the class after calling acts_as_tree:

Public Class Methods

generations() click to toggle source

Returns a hash of all nodes grouped by their level in the tree structure.

Class.generations # => { 0=> [root1, root2], 1=> [root1child1, root1child2, root2child1, root2child2] }

# File lib/acts_as_tree.rb, line 131
def self.generations
  all.group_by{ |node| node.tree_level }
end

Public Instance Methods

acts_as_tree(options = {}) click to toggle source

Configuration options are:

  • primary_key - specifies the column name for relations

    (default: +id+)
  • foreign_key - specifies the column name to use for tracking

    of the tree (default: +parent_id+)
  • order - makes it possible to sort the children according to

    this SQL snippet.
  • counter_cache - keeps a count in a children_count column

    if set to +true+ (default: +false+). Specify
    a custom column by passing a symbol or string.
# File lib/acts_as_tree.rb, line 66
    def acts_as_tree(options = {})
      configuration = {
        primary_key:   "id",
        foreign_key:   "parent_id",
        order:         nil,
        counter_cache: nil,
        dependent:     :destroy,
        touch:         false
      }

      configuration.update(options) if options.is_a?(Hash)

      if configuration[:counter_cache] == true
        configuration[:counter_cache] = :children_count
      end

      belongs_to_opts = {
        class_name:    name,
        primary_key:   configuration[:primary_key],
        foreign_key:   configuration[:foreign_key],
        counter_cache: configuration[:counter_cache],
        touch:         configuration[:touch],
        inverse_of:    :children
      }

      belongs_to_opts[:optional] = true if ActiveRecord::VERSION::MAJOR >= 5

      belongs_to :parent, belongs_to_opts

      if ActiveRecord::VERSION::MAJOR >= 4
        has_many :children, lambda { order configuration[:order] },
          class_name:  name,
          primary_key: configuration[:primary_key],
          foreign_key: configuration[:foreign_key],
          dependent:   configuration[:dependent],
          inverse_of:  :parent
      else
        has_many :children, class_name:  name,
          primary_key: configuration[:primary_key],
          foreign_key: configuration[:foreign_key],
          order:       configuration[:order],
          dependent:   configuration[:dependent],
          inverse_of:  :parent
      end

      class_eval <<-EOV
        include ActsAsTree::InstanceMethods

        def self.default_tree_order
          order_option = #{configuration[:order].inspect}
          order(order_option)
        end

        def self.root
          self.roots.first
        end

        def self.roots
          where(:#{configuration[:foreign_key]} => nil).default_tree_order
        end
      EOV

      # Returns a hash of all nodes grouped by their level in the tree structure.
      #
      # Class.generations # => { 0=> [root1, root2], 1=> [root1child1, root1child2, root2child1, root2child2] }
      def self.generations
        all.group_by{ |node| node.tree_level }
      end


      if configuration[:counter_cache]
        after_update :update_parents_counter_cache

        def children_counter_cache_column
          reflect_on_association(:parent).counter_cache_column
        end

        def leaves
          where(children_counter_cache_column => 0).default_tree_order
        end

      else
        # Fallback to less efficient ways to find leaves.
        class_eval <<-EOV
          def self.leaves
            internal_ids = select(:#{configuration[:foreign_key]}).where(arel_table[:#{configuration[:foreign_key]}].not_eq(nil))
            where("\#{connection.quote_column_name('#{configuration[:primary_key]}')} NOT IN (\#{internal_ids.to_sql})").default_tree_order
          end
        EOV
      end
    end
children_counter_cache_column() click to toggle source
# File lib/acts_as_tree.rb, line 139
def children_counter_cache_column
  reflect_on_association(:parent).counter_cache_column
end
leaves() click to toggle source
# File lib/acts_as_tree.rb, line 143
def leaves
  where(children_counter_cache_column => 0).default_tree_order
end