A tree structure for Mongoid documents using the materialized path pattern

• mongoid (>= 4.0, < 9.0)

For a mongoid 3.x compatible version, please use mongoid-tree 1.0.x, for a mongoid 2.x compatible version, please use mongoid-tree 0.7.x.

To install mongoid_tree, simply add it to your Gemfile:

gem 'mongoid-tree', require: 'mongoid/tree'

In order to get the latest development version of mongoid-tree:

gem 'mongoid-tree', git: 'git://github.com/benedikt/mongoid-tree', branch: :main

You might want to add require: nil option and explicitly require 'mongoid/tree' where needed and finally run

bundle install

To fix issues with the ordering of ancestors, mongoid-tree 2.0 introduces a new depth field to the documents that include the Mongoid::Tree module. In case your project uses its own depth field, you can now rely on mongoid-tree to handle this.

Read the API documentation at https://www.rubydoc.info/github/benedikt/mongoid-tree and take a look at the Mongoid::Tree module

class Node
  include Mongoid::Document
  include Mongoid::Tree
end

There are several utility methods that help getting to other related documents in the tree:

Node.root
Node.roots
Node.leaves

node.root
node.parent
node.children
node.ancestors
node.ancestors_and_self
node.descendants
node.descendants_and_self
node.siblings
node.siblings_and_self
node.leaves

In addition it's possible to check certain aspects of the document's position in the tree:

node.root?
node.leaf?
node.depth
node.ancestor_of?(other)
node.descendant_of?(other)
node.sibling_of?(other)

See Mongoid::Tree for more information on these methods.

Mongoid::Tree doesn't order children by default. To enable ordering of tree nodes include the Mongoid::Tree::Ordering module. This will add a position field to your document and provide additional utility methods:

node.lower_siblings
node.higher_siblings
node.first_sibling_in_list
node.last_sibling_in_list

node.move_up
node.move_down
node.move_to_top
node.move_to_bottom
node.move_above(other)
node.move_below(other)

node.at_top?
node.at_bottom?

Example:

class Node
  include Mongoid::Document
  include Mongoid::Tree
  include Mongoid::Tree::Ordering
end

See Mongoid::Tree::Ordering for more information on these methods.

It's possible to traverse the tree using different traversal methods using the Mongoid::Tree::Traversal module.

Example:

class Node
  include Mongoid::Document
  include Mongoid::Tree
  include Mongoid::Tree::Traversal
end

node.traverse(:breadth_first) do |n|
  # Do something with Node n
end

Mongoid::Tree does not handle destroying of nodes by default. However it provides several strategies that help you to deal with children of deleted documents. You can simply add them as before_destroy callbacks.

Available strategies are:

• :nullify_children -- Sets the children's parent_id to null
• :move_children_to_parent -- Moves the children to the current document's parent
• :destroy_children -- Destroys all children by calling their #destroy method (invokes callbacks)
• :delete_descendants -- Deletes all descendants using a database query (doesn't invoke callbacks)

Example:

class Node
  include Mongoid::Document
  include Mongoid::Tree

  before_destroy :nullify_children
end

There are two callbacks that are called before and after the rearranging process. This enables you to do additional computations after the documents position in the tree is updated. See Mongoid::Tree for details.

Example:

class Page
  include Mongoid::Document
  include Mongoid::Tree

  after_rearrange :rebuild_path

  field :slug
  field :path

  private

  def rebuild_path
    self.path = self.ancestors_and_self.collect(&:slug).join('/')
  end
end

Mongoid::Tree currently does not validate the document's children or parent associations by default. To explicitly enable validation for children and parent documents it's required to add a validates_associated validation.

Example:

class Node
  include Mongoid::Document
  include Mongoid::Tree

  validates_associated :parent, :children
end

mongoid-tree is on GitHub Actions running the specs on Ruby 2.7-3.2 and Mongoid 4.x-8.x.

See https://github.com/benedikt/mongoid-tree/issues

See https://github.com/benedikt/mongoid-tree and feel free to fork it!

See a list of all contributors at https://github.com/benedikt/mongoid-tree/contributors. Thanks a lot everyone!

Copyright (c) 2010-2023 Benedikt Deicke. See LICENSE for details.