Hi Folks,
I just joined the list and have begun my initial explorations of neo4j.
I've been able to build a simple directed graph database, create a
TraversalDescription, traverse the graph and write a Pruner.
I then started to explore the graph algorithms, starting with the
"shortest path" algorithm from the GraphAlgoFactory class. Although I
can traverse my graph using a Traverser, I cannot seem to be able to get
a path from using the GraphAlgoFactory.
The path that is always returned by the following statement is always
null, even though I know the path exists using the Traverser.
path = pathFinder.findSinglePath(startNode, endNode);
Here is the snapshot of my class, first using the Traverser, and then
trying to use the Graph Algorithms. Any insight into what I'm
overlooking would be greatly appreciated.
public class FindShortestPath {
public static void main(String[] args) {
String databaseLocation =
"/home/neo4j/simpleDirectedGraphDb";
GraphDatabaseService graphDb = new
EmbeddedGraphDatabase(databaseLocation);
IndexService indexService = new
LuceneIndexService(graphDb);
Transaction tx = graphDb.beginTx();
PropertyContainer propertyContainer;
StringBuffer pathBuffer;
try {
String startName = "Jack";
String endName = "Jill";
Node startNode =
indexService.getSingleNode("NAME", startName);
Node endNode =
indexService.getSingleNode("NAME", endName);
System.out.println("StartNode: " +
startNode.getProperty("NAME"));
System.out.println("EndNode: " +
endNode.getProperty("NAME"));
// Traverse the Graph - Traversing is
successfull here....
TraversalDescription td = new
TraversalDescriptionImpl();
td = td.depthFirst();
td = td.relationships(RelationshipTypes.LIKES,
Direction.OUTGOING);
td = td.relationships(RelationshipTypes.KNOWS,
Direction.OUTGOING);
Traverser traverser = td.traverse(startNode);
Iterator<Path> traversalIterator =
traverser.iterator();
int pathCount = 0;
Path path = null;
while (traversalIterator.hasNext()) {
pathCount++;
path = (Path) traversalIterator.next();
Iterable<Node> nodeIterable =
path.nodes();
Iterator<Node> nodeIterator =
nodeIterable.iterator();
pathBuffer = new StringBuffer();
while (nodeIterator.hasNext()) {
Node node = (Node)
nodeIterator.next();
pathBuffer.append(node.getProperty("NAME") + "->");
}
System.out.println("TRAVERSE: " +
pathBuffer.toString());
}
// Start Graph Algorithm
StandardExpander expander = new
OrderedByTypeExpander();
expander.add(RelationshipTypes.KNOWS,
Direction.OUTGOING);
expander.add(RelationshipTypes.LIKES,
Direction.OUTGOING);
PathFinder<Path> pathFinder =
GraphAlgoFactory.shortestPath(expander, 20);
path = pathFinder.findSinglePath(startNode,
endNode);
/* PATH IS ALWAYS NULL HERE */
if (path != null) {
Iterator<PropertyContainer> pathIterator
= path.iterator();
pathBuffer = new StringBuffer();
while (pathIterator.hasNext()) {
propertyContainer =
(PropertyContainer) pathIterator.next();
String name = (String)
propertyContainer.getProperty("NAME");
pathBuffer.append(name + "->");
}
System.out.println("Single Path: " +
pathBuffer.toString());
} else {
System.out.println("Could not find a
path, path is null");
}
tx.success();
} catch (Exception e) {
e.printStackTrace();
graphDb.shutdown();
}
graphDb.shutdown();
}
}
Thanks!
-- Bernie
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