A Graph Database for JRuby. It uses the java lib neo4j as storage and lucene for quering/indexing
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Welcome to Neo4j.rb

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.


Version >= 2.0

  • Blog

  • Github Wiki

  • YARD

  • RSpecs - There are 2023 RSpecs (478/neo4j-core, 425/neo4j-wrapper and 1120/this gem - 2012 April)

Version < 2.0.alpha.5

Presentation Materials and other URLs

Why Neo4j.rb or a Graph Database ?

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.

Public API

The neo4j gem depends on the neo4j-wrapper and neo4j-core gems.

neo4j gem







Example of using Neo4j with Rails 3 (ActiveModel)

class User < Neo4j::Rails::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

  # add an exact lucene index on the email property
  property :email, :index => :exact


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


u = User.new(:name => 'kalle', :age => 42, :email => "bla@foo.com")

Make sure you are using JRuby !

Generate a Rails Application

Example of creating an Neo4j Application from scratch: (make sure you have installed JRuby version >= 1.6.2)

gem install rails
rails new myapp -m http://andreasronge.github.com/neo4j/rails.rb
cd myapp
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





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

# 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'

The Neo4j::NodeMixin and Neo4j::RelationshipMixin is implemented in the neo4j-wrapper gem

neo4j-core gem

Neo4j::Node The Java Neo4j Node

Neo4j::Relationship The Java Relationship

Neo4j The Database

Neo4j::Cypher Cypher DSL, see RSpec spec/neo4j/cypher_spec

Neo4j::Algo Included algorithms, like shortest path


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]}"}

The Neo4j::Node and Neo4j::Relationship is implemented in the neo4j-core gem.


As you seen above, neo4j.rb consists of a three layers API:

  • Layer 1, neo4j-core. For interacting with the basic building blocks of the graph database (node, properties and relationship), see Neo4j::Node and Neo4j::Relationship classes.

  • Layer 2, neo4j-wrapper. A binding API to Ruby objects, see Neo4j::NodeMixin and Neo4j::RelationshipMixin modules.

  • Layer 3, neo4j. An implementation of the Rails Active Model and a subset of the Active Record API, see Neo4j::RailsNode and Neo4j::RailsRelationship class.

Notice that you can always access the lower layers if you want to do some more advanced. You can even access the Java API directly.

Project information


Development configuration - You can configure Neo4j through the Neo4j::Config object.

Neo4j::Config[:storage_path] = "/var/neo4j"

Configuring Neo4j from Rails - When using Neo4j.rb from rails you can use the normal rails configuration to set Neo4j configuration.

config.neo4j.storage_path = "#{config.root}/db/neo4j"


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).


Notice there are different license for the neo4j-community, neo4j-advanced and neo4j-enterprise jar gems. Only the neo4j-community gem is by default required.