Neo4j::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

Property

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.

Property Index

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

Property Constraint

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.

Property 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.

Callbacks

Implements like Active Records the following callback hooks:

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

created_at, updated_at

See http://neo4j.rubyforge.org/classes/Neo4j/Rails/Timestamps.html

class Blog
  include Neo4j::ActiveNode
  property :updated_at  # will automatically be set when model changes
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 Unique IDs for details.

Associations

What follows is an overview of adding associations to models. For more detailed information, see Declared Relationships.

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
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