mm-tree

IMPORTANT NOTE: Current master branch is unstable, and is not recommended for production sites. Due to MM not being actively maintained, a monogid version is in the works.

This is a tree structure for MongoMapper documents that support rational numbers for positioning. Read about rational numbers in tree structures here: http://arxiv.org/pdf/0806.3115v1.pdf

The reason for the changed implementation to use rational numbers is to be able to query a tree and get the tree structure by sorting on the rational number. It also makes it easy to query parts of a tree as well.

Rational numbers is even better than left/right trees, as you can remove parts of a tree or a node without reordering the entire tree. It is a bit more complicated, but there are some really good benefits.

Latest stable release:

gem 'mm-tree'

For latest edge version:

gem 'mm-tree', :git => 'http://github.com/leifcr/mm-tree.git'

This gem only supports the following versions:

• mongomapper >= 0.13
• ruby >= 2.0
• rails >= 3.2

_Note: If you are using mongo_mapper < 0.13, ruby < 2.0 or rails < 3.2 you have to use version 0.1.4.

Enable the tree functionality by adding the plugin on your model

class Category
  include MongoMapper::Document
  plugin  MongoMapper::Plugins::Tree

  key :name, String
end

Note: Rational numbers positioning is enabled by default.

This adds one embedded tree_info document (non-changeable) and the following class attributes:

• tree_parent_id_field overrides the field used for parent_id (default: parent_id)
• tree_search_class expects a Class that is a MongoMapper::Document to be used for search (So you can have one collection with inherited models and trees for each model, not conflicting with each other)
• tree_use_rational_numbers use rational numbers for sorting. set to false if you don't want it.
• tree_order controls the order if rational numbers aren't used (format :field_name.[asc|desc]), else soriting is by rational numbers.

If you want to use explicit tree_order, you have to set tree_use_rational_numbers to false.

Not using rational numbers, sorting by name, and using a different ID field.

class Category
  include MongoMapper::Document
  plugin  MongoMapper::Plugins::Tree
  self.tree_parent_id_field      = "my_super_parent_id"
  self.tree_use_rational_numbers = false
  self.tree_order                = :name.asc

  key :name, String
end

Using rational numbers, and using search classes to have inherited models in same collection but different trees:

class Shape
  include MongoMapper::Document
  plugin  MongoMapper::Plugins::Tree
  self.tree_search_class = Shape

  key :name, String
end

class Circle < Shape
  self.tree_search_class = Circle
end

class Square < Shape
  self.tree_search_class = Square
end

Using rational numbers, and using search classes to have inherited models in same collection and same tree:

class Shape
  include MongoMapper::Document
  plugin  MongoMapper::Plugins::Tree
  self.tree_search_class = Shape

  key :name, String
end

class Circle < Shape
end

class Square < Shape
end

To move a child node from one parent to another you can do either move to a specific rational number, or just set the parent.

Move using parent

node_1      = Category.create(:name => "Node 1")
node_1_1    = Category.create(:name => "Node 1.1", :parent => @node_1)
node_2      = Category.create(:name => "Node 2")
node_1_1.parent = node_2
node_1_1.save
node_1_1.parent.name # => "Node 2"

Move using rational values (nv/dv)

node_1      = Category.create(:name => "Node 1")
node_1_1    = Category.create(:name => "Node 1.1", :parent => @node_1)
node_2      = Category.create(:name => "Node 2")
node_2.set_position(node_1_1.tree_info.nv, node_1_1.tree_info.dv) # move to position of node_1_1
node_2.save
node_2.siblings.first.name # => "Node 1.1"
node_2.parent.name # => "Node 1"
# Node 2 is now in front of Node 1.1 as it has taken node 1.1's place.

Check test_order.rb, test_tree.rb and test_search_class.rb for more examples and details on usage.

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Send me a pull request, if you have features you like to see implemented.

Jakob Vidmar (For the original MongoMapper Tree) Joel Junström (I based this tree on his refactoring of Jakobs MongoMapper Tree) MongoMapper devels (John Nunemaker, Brandon Keepers, Chris Heald and others)

Original ideas are Copyright Jakob Vidmar and Joel Junström. Please see their github repositories for details Copyright (c) 2013 Leif Ringstad. See LICENSE for details.