ActiveNode

ActiveNode is the ActiveRecord replacement module for Rails. Its syntax should be familiar for ActiveRecord users but has some unique qualities.

To use ActiveNode, include Neo4j::ActiveNode in a class.

class Post
  include Neo4j::ActiveNode
end

Properties

All properties for Neo4j::ActiveNode objects must be declared (unlike neo4j-core nodes). Properties are declared using the property method which is the same as attribute from the active_attr gem.

Example:

class Post
  include Neo4j::ActiveNode
  property :title, index: :exact
  property :text, default: 'bla bla bla'
  property :score, type: Integer, default: 0

  validates :title, :presence => true
  validates :score, numericality: { only_integer: true }

  before_save do
    self.score = score * 100
  end

  has_n :friends
end

Properties can be indexed using the index argument on the property method, see example above.

See the Properties section for additional information.

See also

There is also a screencast available reviewing properties:

Labels

By default ActiveNode takes your model class’ name and uses it directly as the Neo4j label for the nodes it represents. This even includes using the module namespace of the class. That is, the class MyClass in the MyModule module will have the label MyModule::MyClass. To change this behavior, see the module_handling configuration variable.

Additionally you can change the name of a particular ActiveNode by using mapped_label_name like so:

class Post
  include Neo4j::ActiveNode

  self.mapped_label_name = 'BlogPost'
end

Indexes

To declare a index on a property

class Person
  include Neo4j::ActiveNode
  property :name, index: :exact
end

Only exact index is currently possible.

Indexes can also be declared like this:

class Person
  include Neo4j::ActiveNode
  property :name
  index :name
end

Constraints

You can declare that a property should have a unique value.

class Person
  property :id_number, constraint: :unique # will raise an exception if id_number is not unique
end

Notice an unique validation is not enough to be 100% sure that a property is unique (because of concurrency issues, just like ActiveRecord). Constraints can also be declared just like indexes separately, see above.

Labels

The class name maps directly to the label. In the following case both the class name and label are Post

class Post
  include Neo4j::ActiveNode
end

If you want to specify a different label for your class you can use mapped_label_name:

class Post
  include Neo4j::ActiveNode

  self.mapped_label_name = 'BlogPost'
end

If you would like to use multiple labels you can use class inheritance. In the following case object created with the Article model would have both Post and Article labels. When querying Article both labels are required on the nodes as well.

class Post
  include Neo4j::ActiveNode
end

class Article < Post
end

Serialization

Pass a property name as a symbol to the serialize method if you want to save a hash or an array with mixed object types* to the database.

class Student
  include Neo4j::ActiveNode

  property :links

  serialize :links
end

s = Student.create(links: { neo4j: 'http://www.neo4j.org', neotech: 'http://www.neotechnology.com' })
s.links
# => {"neo4j"=>"http://www.neo4j.org", "neotech"=>"http://www.neotechnology.com"}
s.links.class
# => Hash

Neo4j.rb serializes as JSON by default but pass it the constant Hash as a second parameter to serialize as YAML. Those coming from ActiveRecord will recognize this behavior, though Rails serializes as YAML by default.

Neo4j allows you to save Ruby arrays to undefined or String types but their contents need to all be of the same type. You can do user.stuff = [1, 2, 3] or user.stuff = [“beer, “pizza”, “doritos”] but not user.stuff = [1, “beer”, “pizza”]. If you wanted to do that, you could call serialize on your property in the model.

Enums

You can declare special properties that maps an integer value in the database with a set of keywords, like ActiveRecord::Enum

class Media
  include Neo4j::ActiveNode

  enum type: [:image, :video, :unknown]
end

media = Media.create(type: :video)
media.type
# => :video
media.image!
media.image?
# => true

For every keyword specified, a couple of methods are defined to set or check the current enum state (In the example: image?, image!, video?, ... ).

With options _prefix and _suffix, you can define how this methods are generating, by adding a prefix or a suffix.

With _prefix: :something, something will be added before every method name.

Media.enum type: [:image, :video, :unknown], _prefix: :something
media.something_image?
media.something_image!

With _suffix: true, instead, the name of the enum is added in the bottom of all methods:

Media.enum type: [:image, :video, :unknown], _suffix: true
media.image_type?
media.image_type!

You can find elements by enum value by using a set of scope that enum defines:

Media.image
# => CYPHER: "MATCH (result_media:`Media`) WHERE (result_media.type = 0)"
Media.video
# => CYPHER: "MATCH (result_media:`Media`) WHERE (result_media.type = 1)"

Or by using where:

Media.where(type: :image)
# => CYPHER: "MATCH (result_media:`Media`) WHERE (result_media.type = 0)"
Media.where(type: [Media.types[:image], Media.types[:video]])
# => CYPHER: "MATCH (result_media:`StoredFile`) WHERE (result_media.type IN [0, 1])"
Media.as(:m).where('m.type <> ?', Media.types[:image])
# => CYPHER: "MATCH (result_media:`StoredFile`) WHERE (result_media.type <> 0)"

By default, every enum property will be defined as unique, to improve query performances. If you want to disable this, simply pass _index: false to enum:

class Media
  include Neo4j::ActiveNode

  enum type: [:image, :video, :unknown], _index: false
end

Wrapping

When loading a node from the database there is a process to determine which ActiveNode model to choose for wrapping the node. If nothing is configured on your part then when a node is created labels will be saved representing all of the classes in the hierarchy.

That is, if you have a Teacher class inheriting from a Person model, then creating a Person object will create a node in the database with a Person label, but creating a Teacher object will create a node with both the Teacher and Person labels.

If there is a value for the property defined by class_name_property then the value of that property will be used directly to determine the class to wrap the node in.

Callbacks

Implements like Active Records the following callback hooks:

  • initialize
  • validation
  • find
  • save
  • create
  • update
  • destroy

created_at, updated_at

class Blog
  include Neo4j::ActiveNode

  include Neo4j::Timestamps # will give model created_at and updated_at timestamps
  include Neo4j::Timestamps::Created # will give model created_at timestamp
  include Neo4j::Timestamps::Updated # will give model updated_at timestamp
end

Validation

Support the Active Model validation, such as:

validates :age, presence: true validates_uniqueness_of :name, :scope => :adult

id property (primary key)

Unique IDs are automatically created for all nodes using SecureRandom::uuid. See UniqueIDs for details.

Associations

has_many and has_one associations can also be defined on ActiveNode models to make querying and creating relationships easier.

class Post
  include Neo4j::ActiveNode
  has_many :in, :comments, origin: :post
  has_one :out, :author, type: :author, model_class: :Person
end

class Comment
  include Neo4j::ActiveNode
  has_one :out, :post, type: :post
  has_one :out, :author, type: :author, model_class: :Person
end

class Person
  include Neo4j::ActiveNode
  has_many :in, :posts, origin: :author
  has_many :in, :comments, origin: :author

  # Match all incoming relationship types
  has_many :in, :written_things, type: false, model_class: [:Post, :Comment]

  # or if you want to match all model classes:
  # has_many :in, :written_things, type: false, model_class: false

  # or if you watch to match Posts and Comments on all relationships (in and out)
  # has_many :both, :written_things, type: false, model_class: [:Post, :Comment]
end

You can query associations:

post.comments.to_a          # Array of comments
comment.post                # Post object
comment.post.comments       # Original comment and all of it's siblings.  Makes just one query
post.comments.authors.posts # All posts of people who have commented on the post.  Still makes just one query

You can create associations

post.comments = [comment1, comment2]  # Removes all existing relationships
post.comments << comment3             # Creates new relationship

comment.post = post1                  # Removes all existing relationships

Dependent Associations

Similar to ActiveRecord, you can specify four dependent options when declaring an association.

class Route
  include Neo4j::ActiveNode
  has_many :out, :stops, type: :STOPPING_AT, dependent: :delete_orphans
end

The available options are:

  • :delete, which will delete all associated records in Cypher. Callbacks will not be called. This is the fastest method.
  • :destroy, which will call each on the association and then destroy on each related object. Callbacks will be called. Since this happens in Ruby, it can be a very expensive procedure, so use it carefully.
  • :delete_orphans, which will delete only the associated records that have no other relationships of the same type.
  • :destroy_orphans, same as above, but it takes place in Ruby.

The two orphan-destruction options are unique to Neo4j.rb. As an example of when you’d use them, imagine you are modeling tours, routes, and stops along those routes. A tour can have multiple routes, a route can have multiple stops, a stop can be in multiple routes but must have at least one. When a route is destroyed, :delete_orphans would delete only those related stops that have no other routes.

See also

There is also a screencast available reviewing associations:

See also

#has_many and #has_one

Creating Unique Relationships

By including the unique option in a has_many or has_one association’s method call, you can change the Cypher used to create from “CREATE” to “CREATE UNIQUE.”

has_many :out, :friends, type: 'FRIENDS_WITH', model_class: :User, unique: true

Instead of true, you can give one of three different options:

  • :none, also used true is given, will not include properties to determine whether ot not to create a unique relationship. This means that no more than one relationship of the same pairing of nodes, rel type, and direction will ever be created.
  • :all, which will include all set properties in rel creation. This means that if a new relationship will be created unless all nodes, type, direction, and rel properties are matched.
  • {on: [keys]} will use the keys given to determine whether to create a new rel and the remaining properties will be set afterwards.

Eager Loading

ActiveNode supports eager loading of associations in two ways. The first way is transparent. When you do the following:

person.blog_posts.each do |post|
  puts post.title
  puts "Tags: #{post.tags.map(&:name).join(', ')}"
  post.comments.each do |comment|
    puts '  ' + comment.title
  end
end

Only three Cypher queries will be made:

  • One to get the blog posts for the user
  • One to get the tags for all of the blog posts
  • One to get the comments for all of the blog posts

While three queries isn’t ideal, it is better than the naive approach of one query for every call to an object’s association (Thanks to DataMapper for the inspiration).

For those times when you need to load all of your data with one Cypher query, however, you can do the following to give ActiveNode a hint:

person.blog_posts.with_associations(:tags, :comments).each do |post|
  puts post.title
  puts "Tags: #{post.tags.map(&:name).join(', ')}"
  post.comments.each do |comment|
    puts '  ' + comment.title
  end
end

All that we did here was add .with_associations(:tags, :comments). In addition to getting all of the blog posts, this will generate a Cypher query which uses the Cypher COLLECT() function to efficiently roll-up all of the associated objects. ActiveNode then automatically structures them into a nested set of ActiveNode objects for you.