The traversals from the Matrix example above, this time using the new traversal API:

Friends and friends of friends. 

private static Traverser getFriends( final Node person )
{
    TraversalDescription td = Traversal.description()
            .breadthFirst()
            .relationships( RelTypes.KNOWS, Direction.OUTGOING )
            .evaluator( Evaluators.excludeStartPosition() );
    return td.traverse( person );
}

Let’s perform the actual traversal and print the results:

Traverser friendsTraverser = getFriends( neoNode );
int numberOfFriends = 0;
for ( Path friendPath : friendsTraverser )
{
    System.out.println( "At depth " + friendPath.length() + " => "
                        + friendPath.endNode()
                                .getProperty( "name" ) );
}

Who coded the Matrix? 

private static Traverser findHackers( final Node startNode )
{
    TraversalDescription td = Traversal.description()
            .breadthFirst()
            .relationships( RelTypes.CODED_BY, Direction.OUTGOING )
            .relationships( RelTypes.KNOWS, Direction.OUTGOING )
            .evaluator(
                    Evaluators.returnWhereLastRelationshipTypeIs( RelTypes.CODED_BY ) );
    return td.traverse( startNode );
}

Print out the result:

Traverser traverser = findHackers( getNeoNode() );
int numberOfHackers = 0;
for ( Path hackerPath : traverser )
{
    System.out.println( "At depth " + hackerPath.length() + " => "
                        + hackerPath.endNode()
                                .getProperty( "name" ) );
}

Full source code: MatrixNewTravTest.java

This example shows how to use a path context holding a representation of a path.

Create a toy graph. 

Node A = db.createNode();
Node B = db.createNode();
Node C = db.createNode();
Node D = db.createNode();
A.createRelationshipTo( B, REL1 );
B.createRelationshipTo( C, REL2 );
C.createRelationshipTo( D, REL3 );
A.createRelationshipTo( C, REL2 );

Now, the order of relationships (REL1 → REL2 → REL3) is stored in an ArrayList. Upon traversal, the Evaluator can check against it to ensure that only paths are included and returned that have the predefined order of relationships:

Walk the path. 

final ArrayList<RelationshipType> orderedPathContext = new ArrayList<RelationshipType>();
orderedPathContext.add( REL1 );
orderedPathContext.add( withName( "REL2" ) );
orderedPathContext.add( withName( "REL3" ) );
TraversalDescription td = Traversal.description().evaluator(
        new Evaluator()
        {
            @Override
            public Evaluation evaluate( final Path path )
            {
                if ( path.length() == 0 )
                {
                    return Evaluation.EXCLUDE_AND_CONTINUE;
                }
                String currentName = path.lastRelationship().getType().name();
                String relationshipType = orderedPathContext.get(
                        path.length() - 1 ).name();
                if ( path.length() == orderedPathContext.size() )
                {
                    if ( currentName.equals( relationshipType ) )
                    {
                        return Evaluation.INCLUDE_AND_PRUNE;
                    }
                    else
                    {
                        return Evaluation.EXCLUDE_AND_PRUNE;
                    }
                }
                else
                {
                    if ( currentName.equals( relationshipType ) )
                    {
                        return Evaluation.EXCLUDE_AND_CONTINUE;
                    }
                    else
                    {
                        return Evaluation.EXCLUDE_AND_PRUNE;
                    }
                }
            }
        } );
Traverser t = td.traverse( db.getNodeById( 1 ) );
for ( Path path : t )
{
    System.out.println( path );
}

Full source code: OrderedPathTest.java

Figure 4.5. Social network data model

The data model for a social network is pretty simple: Persons with names and StatusUpdates with timestamped text. These entities are then connected by specific relationships.

The StatusUpdate list for a Person is a linked list. The head of the list (the most recent status) is found by following status. Each subsequent StatusUpdate is connected by next.

Here’s an example where Andreas Kollegger micro-blogged his way to work in the morning:

To read the status updates, we can create a traversal, like so:

TraversalDescription traversal = Traversal.description().
        depthFirst().
        relationships( NEXT ).
        filter( Traversal.returnAll() );

This gives us a traverser that will start at one StatusUpdate, and will follow the chain of updates until they run out. Traversers are lazy loading, so it’s performant even when dealing with thousands of statuses - they are not loaded until we actually consume them.

Once we have friends, and they have status messages, we might want to read our friends status' messages, in reverse time order - latest first. To do this, we go through these steps:

Animated, the sequence looks like this.

The code looks like:

PositionedIterator<StatusUpdate> first = statuses.get(0);
StatusUpdate returnVal = first.current();

if ( !first.hasNext() )
{
    statuses.remove( 0 );
}
else
{
    first.next();
    sort();
}

return returnVal;

Full source code: socnet