Neo4j::Core Cypher

“Cypher” is a declarative graph query language that allows for expressive and efficient querying of the graph store without having to write traversals through the graph structure in code. Neo4j.rb provides two ways of using cypher: express queries as Strings or use the Neo4j.rb Cypher DSL.

Cypher

The cypher language is described here: Neo4j Cypher Docuementation

q = Neo4j._query("START n=node(42) RETURN n")
q.first(:n) #=> the @node
q.columns.first => :n

Cypher DSL

See Neo4j#query method.

Example 5.2. Basic Friend finding based on social neighborhood

See http://docs.neo4j.org/chunked/snapshot/cypher-cookbook-friend-finding.html Let say we want to express the following Cypher Query:

START joe=node(some node id)
MATCH joe-[:knows]->friend-[:knows]->friend_of_friend, joe-[r?:knows]->friend_of_friend
WHERE r IS NULL
RETURN friend_of_friend.name, COUNT(*)
ORDER BY COUNT(*) DESC, friend_of_friend.name

This can be done like this:

Neo4j.query(joe_node) do |joe|
  friends_of_friends = node(:friends_of_friends)
  joe > ':knows' > node(:friend) > ':knows' > friends_of_friends
  r = rel('r?:knows').as(:r)
  joe > r > friends_of_friends
  r.exist?
  ret(friends_of_friends[:name], count).desc(count).asc(friends_of_friends[:name])

Or like this using the outgoing instead of the > operator

 friends_of_friends = joe.outgoing(:knows).outgoing(:knows)
 r = rel('r?:knows').as(:r)
 joe > r > friends_of_friends
 r.exist?
 ret(friends_of_friends[:name], count).desc(count).asc(friends_of_friends[:name])