使用 Gremlin (AWS Neptune)，如何从具有特定条件的起始节点遍历边缘获取长度为 n 的所有路径？

Question

Starting with node 1, I want to return all the paths (edges and vertices, with id/label/properties) within n hops following any outbound edges, or following inbound edges with a property predicate (p > 50).

Ideally the paths shouldn't contain any cycles, so a path shouldn't contain the same node twice.

The property p is not present on every edge.

g.addV().property(id, 1).as('1').
  addV().property(id, 2).as('2').
  addV().property(id, 3).as('3').
  addV().property(id, 4).as('4').
  addV().property(id, 5).as('5').
  addV().property(id, 6).as('6').
  addV().property(id, 7).as('7').
  addV().property(id, 8).as('8').
  addE('pointsAt').from('1').to('2').
  addE('pointsAt').from('3').to('1').
  addE('pointsAt').from('4').to('1').property('p', 10).
  addE('pointsAt').from('5').to('1').property('p', 100).
  addE('pointsAt').from('2').to('6').
  addE('pointsAt').from('7').to('2').
  addE('pointsAt').from('8').to('2').property('p', 100).
  iterate()

Assuming we start at Vertex 1 the paths would look like:

1>2
1>2>6
1>2>8
1>5

• 1-2 is included because it's outbound
• 1-3 is excluded because it is inbound to 1 and doesn't have p
• 1-4 is excluded because it is inbound and (p > 50) is false
• 1-5 is included because it is inbound and (p > 50) is true
• 2-6 is included because it's outbound
• 2-7 is excluded because it is inbound to 2 and doesn't have p
• 2-8 is included because it is inbound to 2 and p > 50

I've experimented with many different approaches and I can't seem to get anything close to what I am looking for.

Answer 1

I believe this is what you're looking for:

g.V(1).
   repeat(
      union(
         outE(),inE().has('p',gt(50))
      ).
      otherV().simplePath()).
   emit().
   times(2).
   path().
      by(valueMap().with(WithOptions.tokens))

The repeat() and times() steps dictate that this is a recursive traversal going to a depth of 2. The union() step and containing arguments follow your requirements to include all outgoing edges and only incoming edges with ap property greater than 50. The emit() step forces the repeat() step to stream all paths as they are found. If you didn't include this, you would only get the paths found of length 2 (declared in the times() step).

To wrap this up, we use path() and by() to output the paths found and all of the ids, labels, and properties for each vertex and edge in the path.

The output of this from the graph that you provided looks like this:

==>[[id:1,label:vertex],[id:0,label:pointsAt],[id:2,label:vertex]]
==>[[id:1,label:vertex],[id:3,label:pointsAt,p:100],[id:5,label:vertex]]
==>[[id:1,label:vertex],[id:0,label:pointsAt],[id:2,label:vertex],[id:4,label:pointsAt],[id:6,label:vertex]]
==>[[id:1,label:vertex],[id:0,label:pointsAt],[id:2,label:vertex],[id:6,label:pointsAt,p:100],[id:8,label:vertex]]