Neo4j v3 Unique IDs

id_property (Primary Key)

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.

To work around this, you can define which key should act as primary key on Neo4j::ActiveNode classes instead of using the internal Neo4j ids. By default, ActiveNode will generate a unique ID using SecureRandom::uuid. The instance methods id and uuid will both 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 Neo4j::Config, Rails configuration, or models themselves. For example see config/application.rb or model

Unique IDs are not generated for relationships or ActiveRel 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 ActiveNode class!

Defining your own ID

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

class Person
  include Neo4j::ActiveNode
  id_property :personal_id, on: :phone_and_name

  property :name
  property :phone

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

A note regarding constraints

By default, a uniqueness constraint will be set for all ID properties. To disable this, you can call id_property with constraint: false in your third param.

class Student
  include Neo4j::ActiveNode
  id_property :uuid, auto: :uuid, constraint: :false
end

Of course, you can also use on: :method_name. Omitting the constraint option will set a constraint.

Adding IDs to Existing Data

A migration task is in place if you have old or imported data in need of IDs. See the add_id_property migration.

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 creates a uuid index and a uuid unique constraint on every ActiveNode. 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

schema

Step 2: Clean up any indexes that are not unique

DROP INDEX ON :Tag(uuid);
CREATE CONSTRAINT ON (n:Tag) ASSERT n.uuid IS UNIQUE;

Step 3: Add an id_property to your ActiveNode

id_property :uuid, auto: :uuid

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