Neoid

This gem is not stable. There are currently no stable versions. We're working on fixing this right now. Apologies.

Make your ActiveRecords stored and searchable on Neo4j graph database, in order to make fast graph queries that MySQL would crawl while doing them. Originally by @elado.

Neoid is to Neo4j as Sunspot is to Solr. You get the benefits of Neo4j's speed while keeping your schema on your RDBMS.

Neoid does not require JRuby. It's based on the Neography gem which uses Neo4j's REST API.

Neoid offers querying Neo4j for IDs of objects and then fetch them from your RDBMS, or storing all desired data on Neo4j.

Important: If you are hosting your application on Heroku with Neoid, GrapheneDB does support Gremlin code; their add-on is located here. Also be reminded that the Gremlin code is actively being refactored into Cypher.

See Changelog. Including some breaking changes (and solutions) from previos versions.

Add to your Gemfile and run the bundle command to install it.

gem 'neoid'

Requires Ruby 1.9.3 or later and Neo4j 1.9.8.

We're currently working to bump to 2.1.x land, but for now, you have to use 1.9.8. To get started, install neo4j locally in your project with:

gem install neo4j-core --pre
rake neo4j:install[community,1.9.8]
rake neo4j:start

Initializer neography and neoid in an initializer that is prefixed with 01_, such as config/initializers/01_neo4j.rb:

ENV["NEO4J_URL"] ||= "http://localhost:7474"

uri = URI.parse(ENV["NEO4J_URL"])

$neo = Neography::Rest.new(uri.to_s)

Neography.configure do |c|
  c.server = uri.host
  c.port = uri.port

  if uri.user && uri.password
    c.authentication = 'basic'
    c.username = uri.user
    c.password = uri.password
  end
end

Neoid.db = $neo

Neoid.configure do |c|
  # should Neoid create sub-reference from the ref node (id#0) to every node-model? default: true
  c.enable_subrefs = true
end

For nodes, first include the Neoid::Node module in your model:

class User < ActiveRecord::Base
  include Neoid::Node
end

This will help to create/update/destroy a corresponding node on Neo4j when changed are made a User model.

Then, you can customize what fields will be saved on the node in Neo4j, inside neoidable configuration, using field. You can also pass blocks to save content that's not a real column:

class User < ActiveRecord::Base
  include Neoid::Node
  
  neoidable do |c|
    c.field :slug
    c.field :display_name
    c.field :display_name_length do
      self.display_name.length
    end
  end
end

Let's assume that a User can Like Movies:

# user.rb

class User < ActiveRecord::Base
  include Neoid::Node

  has_many :likes
  has_many :movies, through: :likes

  neoidable do |c|
    c.field :slug
    c.field :display_name
  end
end


# movie.rb

class Movie < ActiveRecord::Base
  include Neoid::Node

  has_many :likes
  has_many :users, through: :likes

  neoidable do |c|
    c.field :slug
    c.field :name
  end
end


# like.rb

class Like < ActiveRecord::Base
  belongs_to :user
  belongs_to :movie
end

Now let's make the Like model a Neoid, by including the Neoid::Relationship module, and define the relationship (start & end nodes and relationship type) options with neoidable config and relationship method:

class Like < ActiveRecord::Base
  belongs_to :user
  belongs_to :movie

  include Neoid::Relationship

  neoidable do |c|
    c.relationship start_node: :user, end_node: :movie, type: :likes
  end
end

Neoid adds the methods neo_node and neo_relationships to instances of nodes and relationships, respectively.

So you could do:

user = User.create!(display_name: "elado")
user.movies << Movie.create("Memento")
user.movies << Movie.create("Inception")

user.neo_node                # => #<Neography::Node…>
user.neo_node.display_name   # => "elado"

rel = user.likes.first.neo_relationship
rel.start_node  # user.neo_node
rel.end_node    # user.movies.first.neo_node
rel.rel_type    # 'likes'

If you'd like to save nodes manually rather than after_save, use auto_index: false:

class User < ActiveRecord::Base
  include Neoid::Node
  
  neoidable auto_index: false do |c|
  end
end

user = User.create!(name: "Elad") # no node is created in Neo4j!

user.neo_save # now there is!

You can query with all Neography's API: traverse, execute_query for Cypher, and execute_script for Gremlin.

Nodes and relationships are auto indexed in the node_auto_index and relationship_auto_index indexes, where the key is Neoid::UNIQUE_ID_KEY (which is 'neoid_unique_id') and the value is a combination of the class name and model id, Movie:43, this value is accessible with model.neo_unique_id. So use the constant and this method, never rely on assebling those values on your own because they might change in the future.

That means, you can query like this:

Neoid.db.get_node_auto_index(Neoid::UNIQUE_ID_KEY, user.neo_unique_id)
# => returns a Neography hash

Neoid::Node.from_hash(Neoid.db.get_node_auto_index(Neoid::UNIQUE_ID_KEY, user.neo_unique_id))
# => returns a Neography::Node

If Subreferences are enabled, you can get the subref node and then get all attached nodes:

Neoid.ref_node.outgoing('users_subref').first.outgoing('users').to_a
# => this, according to Neography, returns an array of Neography::Node so no conversion is needed

These examples query Neo4j using Gremlin for IDs of objects, and then fetches them from ActiveRecord with an in query.

Of course, you can store using the neoidable do |c| c.field ... end all the data you need in Neo4j and avoid querying ActiveRecord.

Most liked movies

gremlin_query = <<-GREMLIN
  m = [:]

  g.v(0)
    .out('movies_subref').out
      .inE('likes')
      .inV
      .groupCount(m).iterate()

  m.sort{-it.value}.collect{it.key.ar_id}
GREMLIN

movie_ids = Neoid.db.execute_script(gremlin_query)

Movie.where(id: movie_ids)

Side note: the resulted movies won't be sorted by like count because the RDBMS won't necessarily do it as we passed a list of IDs. You can sort it yourself with array manipulation, since you have the ids.

Movies of user friends that the user doesn't have

Let's assume we have another Friendship model which is a relationship with start/end nodes of user and type of friends,

user = User.find(1)

gremlin_query = <<-GREMLIN
  u = g.idx('node_auto_index').get(unique_id_key, user_unique_id).next()
  movies = []

  u
    .out('likes').aggregate(movies).back(2)
    .out('friends').out('likes')
    .dedup
    .except(movies).collect{it.ar_id}
GREMLIN

movie_ids = Neoid.db.execute_script(gremlin_query, unique_id_key: Neoid::UNIQUE_ID_KEY, user_unique_id: user.neo_unique_id)

Movie.where(id: movie_ids)

Using search block inside a neoidable block, you can store certain fields.

# movie.rb

class Movie < ActiveRecord::Base
  include Neoid::Node

  neoidable do |c|
    c.field :slug
    c.field :name

    c.search do |s|
      # full-text index fields
      s.fulltext :name
      s.fulltext :description

      # just index for exact matches
      s.index :year
    end
  end
end

Records will be automatically indexed when inserted or updated.

# will match all movies with full-text match for name/description. returns ActiveRecord instanced
Movie.neo_search("*hello*").results

# same as above but returns hashes with the values that were indexed on Neo4j
Movie.search("*hello*").hits

# search in multiple types
Neoid.neo_search([Movie, User], "hello")

# search with exact matches (pass a hash of field/value)
Movie.neo_search(year: 2013).results

Full text search with Neoid is very limited and is likely not to develop more than this basic functionality. I strongly recommend using gems like Sunspot over Solr.

Neoid has a batch ability, that is good for mass updateing/inserting of nodes/relationships. It sends batched requests to Neography, and takes care of type conversion (neography batch returns hashes and other primitive types) and "after" actions (via promises).

A few examples, easy to complex:

Neoid.batch(batch_size: 100) do
  User.all.each(&:neo_save)
end

With then:

User.first.name # => "Elad"

Neoid.batch(batch_size: 100) do
  User.all.each(&:neo_save)
end.then do |results|
  # results is an array of the script results from neo4j REST.

  results[0].name # => "Elad"
end

Nodes and relationships in the results are automatically converted to Neography::Node and Neography::Relationship, respectively.

With individual then as well as then for the entire batch:

Neoid.batch(batch_size: 30) do |batch|
  (1..90).each do |i|
    (batch << [:create_node, { name: "Hello #{i}" }]).then { |result| puts result.name }
  end
end.then do |results|
  puts results.collect(&:name)
end

When in a batch, neo_save adds gremlin scripts to a batch, instead of running them immediately. The batch flushes whenever the batch_size option is met. So even if you have 20000 users, Neoid will insert/update in smaller batches. Default batch_size is 200.

If you have an existing database and just want to integrate Neoid, configure the neoidables and run in a rake task or console.

Use batches! It's free, and much faster. Also, you should use includes to incude the relationship edges on relationship entities, so it doesn't query the DB on each relationship.

Neoid.batch do
  [ Like.includes(:user).includes(:movie), OtherRelationshipModel.includes(:from_model).includes(:to_model) ].each { |model| model.all.each(&:neo_save) }

  NodeModel.all.each(&:neo_save)
end

This will loop through all of your relationship records and generate the two edge nodes along with a relationship (eager loading for better performance). The second line is for nodes without relationships.

For large data sets use pagination. Better interface for that in the future.

Whenever the neo_node on nodes or neo_relationship on relationships is called, Neoid checks if there's a corresponding node/relationship in Neo4j (with the auto indexes). If not, it does the following:

1. Ensures there's a sub reference node (read here about sub references), if that option is on.
2. Creates a node based on the ActiveRecord, with the id attribute and all other attributes from neoidable's field list
3. Creates a relationship between the sub reference node and the newly created node
4. Auto indexes a node in the auto index, for fast lookup in the future

Then, when it needs to find it again, it just seeks the auto index with that ActiveRecord id.

Like Nodes, it uses an auto index, to look up a relationship by ActiveRecord id

1. With the options passed in the neoidable, it fetches the start_node and end_node
2. Then, it calls neo_node on both, in order to create the Neo4j nodes if they're not created yet, and creates the relationship with the type from the options.
3. Adds the relationship to the relationship index.

In order to test your app or this gem, you need a running Neo4j database, dedicated to tests.

I use port 7574 for testing.

To run another database locally (read here too):

Copy the entire Neo4j database folder to a different location,

or

symlink bin, lib, plugins, system, copy conf to a single folder, and create an empty data folder.

Then, edit conf/neo4j-server.properties and set the port (org.neo4j.server.webserver.port) from 7474 to 7574 and run the server with bin/neo4j start

In environments/test.rb, add:

ENV["NEO4J_URL"] = 'http://localhost:7574'

In your spec_helper.rb, add the following configurations:

config.before :all do
  Neoid.clean_db(:yes_i_am_sure)
end

config.before :each do
  Neoid.reset_cached_variables
end

Run the Neo4j DB on port 7474, and run rake from the gem folder.

Please create a new issue if you run into any bugs. Contribute patches via pull requests. Write tests and make sure all tests pass.

TO DO

Developed by @elado and @BenMorganIO