What should the behavior be for shortest path from node to itself - BUG

[Jatin Puri]

There is a bug in GraphAlgoFactory (trivial but never the less irritating). Basically if you try finding a single shortest path from a node to itself, it gives following behavior:

Using  `GraphAlgoFactory.astar`, it throws:

org.neo4j.graphdb.NotFoundException: Relationship -1 not found

Using `GraphAlgoFactory.dijskstra`, it returns:

A Path starting (WeightedPath#startNode) from the node and ending (WeightedPath#endNode) at itself but with no relationship between them.

I looked at the source and found the bug in each and was rectifying it. But I am not sure what the behavior should be. 

Documentation says that it should return null if no path is found. But for a path from a node to itself, should we assume it as a self-loop with no weight, given there is no explicit relationship between node to itself? Or is the behavior of `dijkstra` correct? (I think its wrong)

[Mattias Persson]

Yup looks like a bug to me. I'm one of the authors of that algo implementation, so I'll see if I can have a look at it soon.

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Mattias Persson

Neo4j Hacker at Neo Technology

[Jatin Puri]

Hi Mattias,

Thanks for response. I will probably try patching it and send pull request. Also this will get me more involved more in it :)

About the behavior, what should it be? `null` or a path starting from node to itself? I couldn't find relevant documentation for it

Jatin

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Jatin Puri
http://jatinpuri.com

[Mattias Persson]

I think it makes sense to return a path consisting of just the one node that is start/end. Although I don't know if A* has some standard result for this scenario.

Great to hear that you'd like to have a look and dig around yourself! Please ask more questions in this thread if you'd like to get hints about code navigation or the likes.