Data Model + Context + Role

gistfile1.rb

The Context + Roles :

module Contexts

  # Move an area to different points on the tree.
  #
  # This context has multiple entry points for each deviation of moving an area around the tree.
  #
  # The source area can be moved in any of these 3 ways :
  #
  # - Before an existing area.
  # - After an existing area.
  # - Within, ie in the subtree of, an existing area
  #
  class MoveArea < Contexts::Base

    def initialize(area_id, target_area_id)
      area = Area.find area_id
      target_area = Area.find target_area_id
      target_area_parent = target_area.parent

      add_role :source_area, area, MoveableArea
      add_role :target_area, target_area, MoveableAreaTarget
      add_role :parent_of_target_area, target_area_parent, MoveableAreaTarget
    end

    def move_after_target_area
      roles.source_area.move_after_target_area 
    end

    def move_before_target_area
      roles.source_area.move_before_target_area 
    end

    def move_within_target_area
      roles.source_area.move_within_target_area
    end

  end

  module MoveableAreaTarget

    def add_existing_sub_area(area)
      area.parent = self
      area.save!
    end

  end

  # These role methods use some methods that are provided
  # by the 'resort' gem that is used in the Area model : 
  # delete_from_list, append_to, prepend.
  #
  module MoveableArea

    class CantMoveRoot < StandardError ; end 
    class InvalidMoveTarget < StandardError ; end

    def move_after_target_area 
      check_target_area_not_in_subtree
      check_not_root!(self)
      check_not_root!(roles.target_area)

      add_to_parent_of_target_area

      self.append_to(roles.target_area)
    end

    def move_before_target_area
      check_target_area_not_in_subtree
      check_not_root!(self)
      check_not_root!(roles.target_area)

      add_to_parent_of_target_area

      if roles.target_area.previous
        self.append_to(roles.target_area.previous)
      else
        prepend
      end
    end

    def move_within_target_area
      check_target_area_not_in_subtree
      check_not_root!(self)

      delete_from_list
      roles.target_area.add_existing_sub_area(self)
      prepend # This method is from resort! gem, it moves the area to the top of the list.
    end

    private 

    #Add to the parent of the target area if the parent is different to the current parent.
    def add_to_parent_of_target_area
      if self.parent != roles.target_area.parent
        delete_from_list
        roles.parent_of_target_area.add_existing_sub_area(self)
      end
    end

    #Check that area is not the root of the tree
    def check_not_root!(area = self)
      raise CantMoveRoot if area.parent.blank?
    end

    #Check that the target area is not within the subtree of the source area.
    def check_target_area_not_in_subtree
      raise InvalidMoveTarget if self.find_subtree(roles.target_area.id).exists?
    end

  end

------------------------

The Domain Model :

class Area < ActiveRecord::Base

  #https://github.com/codegram/resort
  #Resort sorts elements within a list using a linked list format
  resort!

  # https://github.com/stefankroes/ancestry
  # Ancestry arranges areas into a hierachy/tree of areas.
  # has_ancestry provides the children and subtree methods.
  has_ancestry 

  validates :name, :presence => true

  has_many   :sections

  default_scope where(:expired=>false)

  def find_section(section_id)
    self.sections.where(:id=>section_id).first
  end

  def find_children(area_id)
    self.children.where(:id=>area_id).first
  end

  def find_subtree(area_id)
    self.subtree.where(:id=>area_id).first
  end

  def ordered_sections
    self.sections.ordered
  end

  def ordered_areas
    self.children.ordered
  end

  def expire
    self.update_attribute :expired, true
  end

  def arranged_subtree 
    self.subtree.arrange
  end

  #TODO : make this nicer. The resort! gem automatically calls this #siblings method to determine
  #what elements are in the same list.
  #This method is required by the resort! gem.
  def siblings
    if self.ancestry.blank?
      #Root children have no siblings, do don't return anything.  Fix this ugliness.
      super.where(:ancestry=>"xxxxxxxxxxxxxxxx")
    else 
      #Call the siblings method that is added by the has_ancestry gem.
      super
    end
  end

end


end