Vertex not in descendants

[John Timm]

I am  using the following gremlin (Java DSL) to compute the descendants of a node:

g.V().has("name", "John").repeat(__.in("parent")).emit()

I'd like to get all vertices that are not a descendant of John and I've tried using the not(...) step but can seem to find a working solution.

Thanks,

JT

[Øyvind Sæbø]

Hi, John

Another way to get all the vertices which are descendants of John (you?) would be like this:

g.V().filter(repeat(out("parent")).until(has("name", "John")))

Since this query filters away all nodes which are not descendants of John, rather than searching for them from John, it can more easily be transformed to a query which finds all nodes which are not descendants of John by simply replacing the filter(...) with a not(...), like this:

g.V().not(repeat(out("parent")).until(has("name", "John")))

[John Timm]

Very good! Thanks for the response. One more thing, what if I wanted to include "self" in the set making the query "not descendant or self"?

Thanks,

JT

[John Timm]

It looks like it is just another not in the chain:

g.V().not(repeat(out("parent")).until(has("name", "John"))).not(has("name", "John")

[Øyvind Sæbø]

Yes:)

Alternatively, you could also swap position of the repeat(...) and until(...), so that we check before every parent step if the current node is John, instead of after. Then the code inside not(...) will find John and all his descendants, and the full query will find all nodes except John and his descendants:

g.V().not(until(has("name", "John")).repeat(out("parent")))

[John Timm]

Thanks. I tried this alternative with the Java DSL as follows:

g.V().not(__.until(__.has("name", "John")).repeat(__.out("parent")))

and am getting a syntax error:

The method repeat(Traversal<?,Object>) in the type GraphTraversal<Object,Object> is not applicable for the arguments (GraphTraversal<Vertex,Vertex>). Any one out there using the Java DSL that can help me tweak this one?

Thanks,

JT

[Graham Wallis]

Hi John

I find the following avoids the parameter type warning:

GraphTraversal<Vertex,Object> rt = (__.out("parent");

GraphTraversal<Vertex, Vertex> gt = g.V().not(__.until(__.has("name", "John")).repeat(rt)); 

Even trying to explicitly cast the repeat traversal resulted in warnings for me too. For some reason splitting it apart makes my IDE happier.

All the best 

  Graham

[John Timm]

Graham:

Thanks for the suggestion. I gave it a try and I still get a the following compiler error:

Type mismatch: cannot convert from GraphTraversal<Vertex,Vertex> to GraphTraversal<Vertex,Object>

on this statement:

GraphTraversal<Vertex,Object> rt = __.out("parent");

Any suggestion?

Thanks,

JT

[Nicolas Trangosi]

You could just cast: g.V().not(__.until(__.has("name", "John")).repeat((GraphTraversal) __.out("parent")));

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[Graham Wallis]

Thanks Nicolas

That certainly removes the compiler error - although in my IDE (IJ) I try to strongly type everything to avoid getting “unchecked assignment” warnings.

I’m not really sure how to advise John. 

Best regards

  Graham 

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