Traversal Framework: No public method for creating ResourceIterable

[mcclown]

• Neo4j version: 5.x (tested on 5.5.0 - 5.15.0)
• Java Driver
• Traversal Framework

I originally outlined the issue here https://community.neo4j.com/t/traversal-framework-working-with-resourceiterables/60963

So with the un-deprecation of the Traversal Framework for Neo4j 5.x there were some changes. One of them causes an issue that I can't resolve without using the undocumented internal APIs.

In Neo4j 4.x the following expand method would have worked. I want to filter the relationships that are returned from the expand. This is a simplified version of my actual method but shows the same problem. In reality I'm doing more complex filtering and ordering of the expanded relationships that are returned from this method.

@Override
public ResourceIterable<Relationship> expand(Path path, BranchState<TraverseState> bState)
{
	TraverseState state = state.getState();

	assert path.endNode().hasLabel(Labels.Undefined);

	var concludes = path.endNode().getRelationships(Direction.OUTGOING, RelationshipTypes.CONCLUDES);
	var expansion = new HashSet<Relationship>();

	for(Relationship rel : concludes)
	{
		if(!state.traverseOnce.contains(rel))
		{
			expansion.add(rel);
			state.traverseOnce.add(rel);
		}
	}

	if(expansion.size() > 0)
		return expansion;
	
	return Collections.emptyList();
}

For this code I get errors for both return statements because they're returning Iterables. If I try casting them, then I get runtime errors as the cast fails.

The only way I have gotten this to work is to use org.neo4j.internal.helpers.collection.Iterables, so the return statements become:

• return Iterables.asResourceIterable(expansion);
• return Iterables.emptyResourceIterable();

Now I don't want to have to use this internal API, as it's not supported but I can't find another way with the support API.

I think these static methods should be part of the public API, or another alternative should be made available. Currently there's no way to create a ResourceIterable directly, that I have found.

[ncordon]

Thanks for reporting @mcclown, we'll look into it

[mcclown]

@ncordon Thank you.

Another related item that someone just pointed out on the forums, the documentation of the Traversal Framework API documentation is also incorrect.

The code examples for creating a PathExpander show a very similar example to my use case but the code has the incorrect return type Iterable<Relationship> and wouldn't compile/work because of this. I can't find a way of implementing the example in the documentation without using the internal class/methods mentioned in the initial ticket.

https://neo4j.com/docs/java-reference/current/traversal-framework/traversal_framework_java_api/#_pathexpanderbuilder

[horak90]

Hello, I am having the same issue, are there any news on this topic?