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¶
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 ... end end
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 end
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:
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:
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 end def down raise IrreversibleMigration end end
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 end def down drop_constraint :Tag, :uuid add_index :Tag, :uuid end end
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.