Module: ActsAsTree::ClassMethods

Defined in:
lib/acts_as_tree.rb

Overview

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:

  • siblings - Returns all the children of the parent, excluding

    the current node (<tt>[subchild2]</tt> when called
    on <tt>subchild1</tt>)
    
  • self_and_siblings - Returns all the children of the parent,

    including the current node (<tt>[subchild1, subchild2]</tt>
    when called on <tt>subchild1</tt>)
    
  • ancestors - Returns all the ancestors of the current node

    (<tt>[child1, root]</tt> when called on <tt>subchild2</tt>)
    
  • root - Returns the root of the current node (root

    when called on <tt>subchild2</tt>)
    

Instance Method Summary collapse

Instance Method Details

#acts_as_tree(options = {}) ⇒ Object

Configuration options are:

  • 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+).
    

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# File 'lib/acts_as_tree.rb', line 63

def acts_as_tree(options = {})
  configuration = {
    foreign_key:   "parent_id",
    order:         nil,
    counter_cache: nil,
    dependent:     :destroy
  }

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

  belongs_to :parent, class_name:    name,
    foreign_key:   configuration[:foreign_key],
    counter_cache: configuration[:counter_cache],
    inverse_of:    :children

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

  class_eval <<-EOV
    include ActsAsTree::InstanceMethods

    after_update :update_parents_counter_cache

    def self.roots
      order_option = %Q{#{configuration.fetch :order, "nil"}}
      where(:#{configuration[:foreign_key]} => nil).order(order_option)
    end

    def self.root
      order_option = %Q{#{configuration.fetch :order, "nil"}}
      self.roots.first
    end
  EOV
end