Neo4j is popular Graph Database system that allows you to manipulate data as nodes related with each other. Following a graph approach on data allows you to implement applications with special characteristics such as apps where users are following other users or pages. Actually, it’s almost impossible to simulate a graph data structure with conventional relational databases (SQL) or even with key-value storage systems. Graph databases is a single way to go, at least if you want to be able to scale for users more than your social circle.

Amongst the existing graph databases solutions, neo4j is gaining popularity. This can be because of it’s robust implementation, the complete documentation that the neo4j wiki page [http://wiki.neo4j.org]offers and the hooks for languages such as ruby, java, python.

In our case, the goal is to implement a simple user-following-user Ruby on Rails application that stores the following information in the graph database, neo4j.

First we need to install and use jruby. Relying to rvm we run start with

rvm install jruby

Then we need to generate a gemset for jruby and create a rails app, using this gemset.

rvm use jruby-1.6.3
 
rvm gemset create neotest
 
rvm use jruby-1.6.3@neotest

To hook the neo4j database with ruby, we should install and use (require) the neo4j gemset. So we run

gem install neo4j

Now Let’s run a simple test. Create a file and paste the following code.

require "rubygems"
require "neo4j"
 
#domain model
class Waypoint
  include Neo4j::NodeMixin
  #the persistent properties of this class
  property :name, :lon, :lat
  #friend relationships to other persons
  has_n :roads
  index :name
end
 
#populate the db
Neo4j::Transaction.run do
  #the waypoints
  NYC = Waypoint.new :name=>'New York', :lon=>-74.007124, :lat=>40.714550
  SF  = Waypoint.new :name=>'San Francisco', :lon=>-122.420139, :lat=>37.779600
  SEA = Waypoint.new :name=>'Seattle', :lon=>-122.329439, :lat=>47.603560
  #the roads
  NYC.roads << SF
  NYC.roads << SEA
  SEA.roads << SF
end
Neo4j::Transaction.run do
  #do a fulltext search over all Waypoints
  Waypoint.find(:name => 'New York').each { |x|
    puts "Found Waypoint: #{x.name}"
  }
end

Now save the file as neotest.rb

Go to terminal and run the file

$ jruby neotest.rb.

So now we have all the basic setup to start playing with neo4j graph database and ruby. As I just started messing with neo4j and graph database structure, I promise that there will be many following posts about these topics.