Unique IDs

The database generates unique IDs and they are accessible from all nodes and relationships using the neo_id method. These keys are somewhat volatile and may be reused or change throughout a database’s lifetime, so they are unsafe to use within an application.

Neo4j.rb requires you to define which key should act as primary key on ActiveGraph::Node classes instead of using the internal Neo4j ids. By default, Node will generate a unique ID using SecureRandom::uuid saving it in a uuid property. The instance method id will also point to this.

You can define a global or per-model generation methods if you do not want to use the default. Additionally, you can change the property that will be aliased to the id method. This can be done through Configuration or models themselves.

Unique IDs are not generated for relationships or Relationship models because their IDs should not be used. To query for a relationship, generate a match based from nodes. If you find yourself in situations where you need relationship IDs, you probably need to define a new Node class!

Defining your own ID

The on parameter tells which method is used to generate the unique id.

class Person
  include ActiveGraph::Node
  id_property :personal_id, on: :phone_and_name

  property :name
  property :phone

  def phone_and_name
    self.name + self.phone # strange example ...

Using internal Neo4j IDs as id_property

Even if using internal Neo4j ids is not recommended, you can configure your model to use it:

class Person
  include ActiveGraph::Node
  id_property :neo_id

A note regarding constraints

A constraint is required for the id_property of an Node model. To create constraints, you can run the following command:

rake neo4j:generate_schema_migration[constraint,Model,uuid]

Replacing Model with your model name and uuid with another id_property if you have specified something else. When you are ready you can run the migrations:

rake neo4j:migrate

If you forget to do this, an exception will be raised giving you the appropriate command to generate the migration.

Adding IDs to Existing Data

If you have old or imported data in need of IDs, you can use the built-in populate_id_property migration helper.

Just create a new migration like this and run it:

rails g neo4j:migration PopulateIdProperties
class PopulateIdProperties < ActiveGraph::Migrations::Base
  def up
    populate_id_property :MyModel

  def down
    raise IrreversibleMigration

It will load the model, find its given ID property and generation method, and populate that property on all nodes of that class where an id_property is not already assigned. It does this in batches of up to 900 at a time by default, but this can be changed with the MAX_PER_BATCH environment variable (batch time taken standardized per node will be shown to help you tune batch size for your DB configuration).

Working with Legacy Schemas

If you already were using uuids, give yourself a pat on the back. Unfortunately, you may run into problems with Neo4j.rb v3. Why? By default Neo4j.rb requires a uuid index and a uuid unique constraint on every Node. You can change the name of the uuid by adding id_property as shown above. But, either way, you’re getting uuid as a shadow index for your nodes.

If you had a property called uuid, you’ll have to change it or remove it since uuid is now a reserved word. If you want to keep it, your indexes will have to match the style of the default id_property (uuid index and unique).

You’ll need to use the Neo4J shell or Web Interface.

Step 1: Check Indexes and Constraints

This command will provide a list of indexes and constraints


Step 2: Clean up any indexes that are not unique using a migration

rails g neo4j:migration AddConstraintToTag
class AddConstraintToTag < ActiveGraph::Migrations::Base
  def up
    drop_index :Tag, :uuid
    add_constraint :Tag, :uuid

  def down
    drop_constraint :Tag, :uuid
    add_index :Tag, :uuid

Step 3: Add an id_property to your Node

id_property :uuid, auto: :uuid

Note: If you did not have an index or a constraint, Neo4j.rb will automatically create them for you.