Choose between 2 available edges during traversal

Question

I'm relatively new to Gremlin, and the company I'm with is looking to implement a graph database with some temporary edges within it. Each vertex could have 1 or more edge, and each edge would have a property on it that is essentially isTemporary true/false.

When traversing the graph, if "isTemporary" = true we should follow that edge, otherwise we should follow the edge where "isTemporary" = false.

I.e.,

A-[isTemporary:true, value 1] -> B

A-[isTemporary:false, value 2] -> C

B-[isTemporary: false, value 3] -> D

Running a single gremlin query should return A->B->D in this case.

I've looked through TinkerPop3 documentation, and it seems like "choose" may be what I want to use here, but all the examples seem to return a value, when what I want is a traversal to come back so I can repeatedly act on the traversal.

Any help would be appreciated.

Answer 1

You could be looking for the coalesce step.

Considering this graph:

g.addV().as('a').property('name', 'A').
  addV().as('b').property('name', 'B').
  addV().as('c').property('name', 'C').
  addV().as('d').property('name', 'D').
  addE('someLink').from('a').to('b').
    property('isTemporary', true).property('value', 1).
  addE('someLink').from('a').to('c').
    property('isTemporary', false).property('value', 2).
  addE('someLink').from('b').to('d').
    property('isTemporary', false).property('value', 3)

The following query will return all paths from A to D, attempting to traverse via isTemporary: true edges if present, or via isTemporary: false edges otherwise (coalesce step), iteratively.

g.V().has('name', 'A').
  repeat(
    coalesce(
      outE().has('isTemporary', true).inV(),
      outE().has('isTemporary', false).inV()
    )
  ).
  until(has('name', 'D')).
  path().by('name')

Result:

==>[A,B,D]