Neo4j：后退遍历

Question

Let's assume a very simple example graph of people (as nodes) and KNOWS- and FRIEND_OF-relationships inbetween. Now I want to get every node that KNOWS a random person and is FRIEND_OF (this or) another person. Please consider, that I want to use a traversal to check those relations instead of a simple node.hasRelationship().

Therefore I would describe a TraversalDescription that checks the path-length in its Evaluator and chooses the KNOWS-relation on step 1. If there is one I (automatically) go to the connected KNOWS-node in the path and would then have to make a step back to the outgoing-node. Therefore I would just check when path.length == 2 for incoming KNOWS-relation and set the continue-variable to true if the current traversed node has the id of the path-startnode.

The problem: I never come back to the path-startnode (the one I checked for the KNOWS-relation), it never appears in the evaluator; I also tried to user different UNIQUENESS-parameters but none of then worked.

/edit: Here's my traversal description (pseudo code more or less):

TraversalDescription td = Traversal.description()
    .relationships(RelTypes.KNOWS, Direction.BOTH)
    .relationships(RelTypes.FRIEND_OF, Direction.OUTGOING)
    .uniqueness(Uniqueness.NONE)
    .evaluate(new Evaluator(){
        public Object evaluate(final Path path){
            if (path.length == 0) return EXCLUDE_CONTINUE;
            Relation currentRel = path.lastRelationship();
            boolean continue = false;
            boolean include = false;
            if (path.length == 1){
                // check for outgoing knows-relation
                continue = currentRel.isType(KNOWS) && currentRel.startNode().getId == path.startNode().getId();
            }
            else if (path.length == 2){
                // check for outgoing knows-relation to the original start node
                // SECOND PART OF STATEMENT NEVER GETS TRUE!
                toContinue = currentRel.isType(KNOWS) && currentRel.startNode().getId == path.startNode().getId();
            }
            else if (path.length == 3){
                // ...
            }
            return Evaluation.of(toContinue, include);
        }

Answer 1

try

private static Traverser getHomies(final Node ofPerson) {
        TraversalDescription td = Traversal.description().breadthFirst().relationships(RelTypes.KNOWS, Direction.INCOMING)
                .relationships(RelTypes.FRIEND_OF, Direction.OUTGOING).evaluator(Evaluators.includingDepths(1, 2))
                .evaluator(Evaluators.returnWhereLastRelationshipTypeIs(RelTypes.FRIEND_OF));

        return td.traverse(ofPerson);
    }

Your pseudocode:

• says that no path should be included - field include is everytime false
• your second part of statement is no comparison (==), it is an assignment (=)