HierarchicalDb

This gem has the implementation of Hierarchical databases

Installation

Add this line to your application's Gemfile:

gem 'hierarchical_db'

And then execute:

$ bundle

Or install it yourself as:

$ gem install hierarchical_db

Next you have to use the hierarchical_db generator into your model. For example, if you have a model called Territory (to manage countries, cities and all the other hierarchies) with the following relationship:

class Territory < ActiveRecord::Base
  belongs_to :parent_territory, class_name: 'Territory'
end

You have to execute the generator with the code below:

rails g hierarchical_db territories

Now your model has the attributes lft, rgt and lvl that are essential to the gem work properly.

Next into the model you have to include Hierarchies adding the code below:

class Territory < ActiveRecord::Base
  include HierarchicalDb #we added this
  belongs_to :parent_territory, class_name: 'Territory'
  has_many :territories, class_name: 'Territory', foreign_key: 'parent_territory_id'
end

Finally we add two alias methods that are useful and necessary to deal with hierarchies and his parent method:

class Territory < ActiveRecord::Base
  include HierarchicalDb 
  belongs_to :parent_territory, class_name: 'Territory'
  has_many :territories, class_name: 'Territory', foreign_key: 'parent_territory_id'
  # alias methods
  alias_method :children, :territories #we added this
  alias_method :parent, :parent_territory #we added this

  def parent_key
    'parent_territory_id'
  end
end

Usage

Continuing the example, if you have data inside your Territory model, then you have to execute :

  Territory.sort_tree

This is a Class method and is imperative to use this after load seeds or when you first enter information inside your model. If you don't have any data inside your model this method doesn't have any sense. On the other hand, if you have data inside your model and you has never executed sort_tree then this gem won't work.
Sort_tree initializes your tree and fills lft and rgt attributes with corresponding information.
After execute this command you will able to use all useful methods below ###Example Model For all our examples we will use territories model with the data below:
Territory model has the attributes: name, lft, rgt, lvl, id and parent_territory_id

id	name	lft	rgt	lvl	parent_territory_id
1	Chile	1	8	1	nil
2	Región Metropolitana	6	7	2	1
3	Región del BíoBío	2	5	2	1
4	Concepción	3	4	3	3

Useful Methods

display_tree

This is a Class method and returns graphically and tabulated the entire tree. Example:

Territory.display_tree

It returns:

1-Chile
  3-Región del BíoBío
    4-Concepción
  2-Región Metropolitana

descendants

Returns an array with all childrens order by lft attribute, example:

object.descendants

descendants_count

If you want to know how many descendants has your model, then you can execute:

 object.descendants_count

It returns a number of descendants.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake false to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ginzunza/hierarchical_db. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.