PgLtree

Gem that allows use ltree in ActiveRecord models.

It uses a implementation based around PostgreSQL's ltree data type, associated functions and operators.

Author	Andrei Panamarenka
Version	1.1.0 (Sep 1, 2015)
License	Released under the MIT license.

Installation

Add this line to your application's Gemfile:

gem 'pg_ltree'

And then execute:

$ bundle

Add ltree extension to PostgreSQL:

class AddLtreeExtension < ActiveRecord::Migration
  def change
    reversible do |dir|
      dir.up do
        execute <<-SQL
          CREATE EXTENSION IF NOT EXISTS ltree;
        SQL
      end
      dir.down do
        execute <<-SQL
          DROP EXTENSION IF NOT EXISTS ltree;
        SQL
      end
    end
  end
end

Update your model:

class AnyModel < ActiveRecord::Migration
  def change
    add_column :any_model, :path, :ltree

    add_index :any_model, :path, using: :gist
  end
end

Run migrations:

$ bundle exec rake db:migrate

Usage

  class AnyModel < ActiveRecord::Base
    ltree :path
    # ltree :path, cascade: false # Disable cascade update and delete
  end

  root     = AnyModel.create!(path: 'Top')
  child    = AnyModel.create!(path: 'Top.Science')
  subchild = AnyModel.create!(path: 'Top.Science.Astronomy')

  root.parent   # => nil
  child.parent # => root
  root.children # => [child]
  root.children.first.children.first # => subchild
  subchild.root # => root

For find a lots of additional information about PgLtee see:

• Wiki
• List of methods for work with LTree
• Module SCOPE FOR (For not uniq path in tree)