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Neo4j.rb is a graph database for JRuby.

You can think of Neo4j as a high-performance graph engine with all the features of a mature and robust database. The programmer works with an object-oriented, flexible network structure rather than with strict and static tables — yet enjoys all the benefits of a fully transactional, enterprise-strength database.

It uses two powerful and mature Java libraries:

• Neo4J - for persistence and traversal of the graph

• Lucene for querying and indexing.

• Guides and API

• Blog: Neo4j and Rails 3

Here are some of the major benefits of Neo4j.rb

• Domain Modeling - use the language of a graph (nodes/relationship/properties) to express your domain !

  • Schema Less and Efficient storage of Semi Structured Information

  • No O/R mismatch - very natural to map a graph to an Object Oriented language like Ruby.

• Performance

• Embedded Database - no database tier, easier to install, test, deploy and configure. It is run in the same process as your application.

• Express Queries as Traversals

  • Fast deep traversal instead of slow SQL queries that span many table joins.

  • Very natural to express graph related problem with traversals (recommendation engine, find shortest parth etc..)

• Seamless integration with Ruby on Rails.

• ACID Transaction with rollbacks support.

Example of creating a Neo4j::Node

require "rubygems"
require 'neo4j'

Neo4j::Transaction.run do
  node = Neo4j::Node.new (:name => 'andreas')
  node.outgoing(:friends) << Neo4j::Node.new (:name => 'peter')
  node.outgoing(:friends).each {|node| puts "name #{node[:name]}"}
end

Example of mapping a ruby class to a node and delaring properties and relationships and lucene index.

class Person
  include Neo4j::NodeMixin
  property :name
  property :city

  has_n :friends
  has_one :address
  index :name
end

# assume we have an transaction already running
andreas = Person.new (:name => 'andreas')
andreas.friends << Person.new (:name => 'peter')
andreas.friends.each {|person| puts "name #{person.name}" }
Person.find("name: andreas").first.name # => 'andreas'

Example of using Neo4j with Rails 3 (ActiveModel)

class User < Neo4j::Model
  attr_accessor :password
  attr_accessible :email, :password, :password_confirmation, :pending_account

  after_save   :encrypt_password

  email_regex = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i

  property :email
  index :email

  has_one(:avatar).to(Avator)

  validates :email, :presence => true,:format   => { :with => email_regex }
  validates :email, :uniqueness => true, :unless => :pending_account?
  accepts_nested_attributes_for :avatar, :allow_destroy => true

  ...
end

Example of creating an Neo4j Application from scratch:

gem install rails
rails new myapp -m http://andreasronge.github.com/rails3.rb
cd myapp
bundle
rails generate scaffold User name:string email:string
rails s
open a webbrowser: http://localhost:3000/users

To run it with Tomcat instead of WEBrick

gem install trinidad
trinidad

• Intoduction to Neo4j.rb

• Nordic Ruby 2010 May 21-23

• Neo4j wiki, check the guidelines and domain modeling gallery pages

• GitHub

• Lighthouse Issue Tracking

• Twitter

• IRC - #neo4j @ irc.freenode.net

• Mailing list, [email protected]

Have you found a bug, need help or have a patch ? Just clone neo4j.rb and send me a pull request or email me. Do you need help - send me an email (andreas.ronge at gmail dot com). Please also check/add issues at lighthouse, neo4j.lighthouseapp.com

• Neo4j.rb - MIT, see the LICENSE file github.com/andreasronge/neo4j/tree/master/LICENSE.

• Lucene - Apache, see lucene.apache.org/java/docs/features.html

• Neo4j - Dual free software/commercial license, see neo4j.org/