The power of traversals - Neo4j in Action - page 78

Listing 4.3. Finding movies that have been seen by John's friends

The first part of this code stores the friends of John in the local variable friends ,

, . First, you iterate through all the IS_FRIEND_OF relationships of the starting

node, regardless of their direction . Remember, although the IS_FRIEND_OF rela-
tionship has a starting and an ending node, you can go upstream as well as downstream
to locate friends. But because you don't know whether John is the starting or ending
node of the relationships, you can't use the Relationship.getStartNode() or
Relationship.getEndNode() methods to determine the other participant in the
friendship. Luckily, the Neo4j Core Java API has a solution for that: the Relation-
ship.getOtherNode(Node node) method. This method, given a node on one end
of the relationship, returns the node on the other end. In this case, because you know that
the relationship has one end at the John node, you can use this method to find out John's

friends . Finally, you add the friend node to the local java.lang.Set variable

friends , which you'll use later.

In the second part of the code, you find all the movies John's friends have seen ,

, . For each of the nodes stored in the temporary local variable , you check all out-

going HAS_SEEN relationships . Just as you did in the previous example, you load the