Neo4j::Core Nodes Properties Relationships

Nodes, Properties and Relationships

The Neo4j node space consists of three basic elements: nodes, relationships that connect nodes and properties attached
to both nodes and relationships. All relationships have a type, for example if the node space represents
a social network, a relationship type could be knows. If a relationship of the type knows connects two nodes,
that probably represents two people that know each other. A lot of the semantics, the meaning, of a node space
is encoded in the relationship types of the application.

Creating Nodes

Example of creating a Neo4j::Node

require "rubygems"
require 'neo4j'

Neo4j::Transaction.run do
  node = Neo4j::Node.new
end

TIP: The Neo4j::Node.new does actually return a Java Neo4j org.neo4j.graphdb.Node object which has been modified to fell more rubyish.

Transactions

All Neo4j write operation must be wrapped in a transaction as shown above.
Here is one way of creating transaction:

Neo4j::Transaction.run do
  # neo4j operations goes here
end

Neo4j::Rails::Model#transaction is a convenient wrapper for this.

TIP: The Neo4j::Transaction returns a Java org.neo4j.graph.Transaction for more info see Neo4j Transactions

Properties

Example of setting properties.

Neo4j::Node.new :name=>'foo', :age=>123, :hungry => false, 4 => 3.14
# which is same as the following:
node = Neo4j::Node.new
node[:name] = 'foo'
node[:age]  = 123
node['hungry'] = false
node[4] = 3.14
node[:age] #  => 123

Properties can be of a primitive value (Fixnum, Float, TrueClass, FalseClass, String) and arrays of those primitive values. Also, @Date and DateTime is also possible to save if you declared it, see Type Conversion below.

WARNING: Array Gotchas 1 all items in an array must be of the same type. Array Gotchas 2 you can not change one item in the array (they are mutable), you have to create a new array each time you add, remove, change one item.

Type Conversion

If you declare a type of a property it can be converted into a primitive.
Example

class Person
  include Neo4j::NodeMixin
  property :born, :type => DateTime
end

The born property will be marshalled into a Java long value automatically since there is (by default) a
registered type conversion for DateTime in the Neo4j::Config object under the key conversions.

You can add your own conversion if you want to save a Ruby object with a property.

Creating Relationships

Example of creating an outgoing Neo4j::Relationship from node1 to node2 of type friends

node1 = Neo4j::Node.new
node2 = Neo4j::Node.new
Neo4j::Relationship.new(:friends, node1, node2)
# which is same as
node1.outgoing(:friends) << node2

Accessing Relationships

Example of getting relationships

node1.rels # => an Enumerable of all incoming and outgoing relationship of any type
node1.rel?  # => true if there are any relationship of any type
node1.rels(:friends) # => all relationship of type friends, both incoming and outgoing
node1.rels(:friends).outgoing # => all outgoing relationship of type friends
node1.rel(:both, :best_friend)  # => returns one relationship, nil or throws an exception if there are more the two relationship from this node
node1.rel(:incoming, :best_friend)

Note that _rels takes different arguments from rels!

node1.rels(:both, :friends)

Finding Relationships between two nodes

You can find all relationships between two nodes like this:

node_a.rels.to_other(node_b)  # => an enumerable of all relationship between those two nodes
node_a.rels(:friends).outgoing.to_other(node_b)  # => an enumerable of relationship of only outgoing relationships of type friend

Deleting Relationships between two nodes

You can combine the to_other method with del to delete relationships between two nodes (see above)

node_a.rels.to_other(node_b).del  # => an enumerable of all relationship between those two nodes
node_a.rels(:friends).outgoing.to_other(node_b).del  # => an enumerable of relationship of only outgoing relationships of type friend

Properties on Relationships

Example of setting properties on relationships

rel = node1.rels(:friends).outgoing.first  # get the first relationship object 
rel[:since] = 1982