Mongoid Nested Set
Mongoid Nested Set is an implementation of the nested set pattern for Mongoid. It is a port of AwesomeNestedSet for ActiveRecord. It supports Mongoid 4+ and Rails 4+
Nested Set represents hierarchies of trees in MongoDB using references rather than embedded documents. A tree is stored as a flat list of documents in a collection. Nested Set allows quick, ordered queries of nodes and their descendants. Tree modification is more costly. The nested set pattern is ideal for models that are read more frequently than modified.
For more on the nested set pattern: http://en.wikipedia.org/wiki/Nested_set_model
Installation
Install as Gem
gem install glebtv-mongoid_nested_set
via Gemfile
gem 'glebtv-mongoid_nested_set', '~> 0.7.0'
Usage
To start using Mongoid Nested Set, just declare acts_as_nested_set
on your
model:
class Category
include Mongoid::Document
acts_as_nested_set
end
Creating a root node
root = Category.create(:name => 'Root Category')
Inserting a node
child1 = root.children.create(:name => 'Child Category #1')
child2 = Category.create(:name => 'Child Category #2')
root.children << child2
Deleting a node
child1.destroy
Descendants of a destroyed nodes will also be deleted. By default, descendant's
destroy
method will not be called. To enable calling descendant's destroy
method:
class Category
include Mongoid::Document
acts_as_nested_set :dependent => :destroy
end
Moving a node
Several methods exist for moving nodes:
- move_left
- move_right
- move_to_left_of(other_node)
- move_to_right_of(other_node)
- move_to_child_of(other_node)
- move_to_root
Scopes
Scopes restrict what is considered a list. This is commonly used to represent multiple trees (or multiple roots) in a single collection.
class Category
include Mongoid::Document
acts_as_nested_set :scope => :root_id
end
Conversion from other trees
Coming from acts_as_tree or adjacency list system where you only have parent_id?
No problem. Simply add acts_as_nested_set
and run:
Category.rebuild!
Your tree will be converted to a valid nested set.
Outline Numbering
Mongoid Nested Set can manage outline numbers (e.g. 1.3.2) for your documents if
you wish. Simply add :outline_number_field
:
acts_as_nested_set, :outline_number_field => 'number'
Your documents will now include a number
field (you can call it anything you
wish) that will contain outline numbers.
Don't like the outline numbers format? Simply override outline_number_seperator
,
build_outline_number
, or outline_number_sequence
in your model classes. For
example:
class Category
include Mongoid::Document
acts_as_nested_set :scope => :root_id, :outline_number_field => 'number'
# Use a dash instead of a dot for outline numbers
# e.g. 1-3-2
def outline_number_seperator
'-'
end
# Use 0-based indexing instead of 1-based indexing
# e.g. 1.0
def outline_number_sequence(prev_siblings)
prev_siblings.count
end
end
References
You can learn more about nested sets at:
http://en.wikipedia.org/wiki/Nested_set_model
http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
Contributing to mongoid_nested_set
- Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
- Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
- Fork the project
- Start a feature/bugfix branch
- Commit and push until you are happy with your contribution
- Make sure to add tests for it. This is important so I don't break it in a future version unintentionally.
- Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so I can cherry-pick around it.
Copyright
Copyright (c) 2010 Brandon Turner. See LICENSE.txt for further details.