Modifying vertex properties while traversing

Question

I want to modify some property for all vertices connected via edges with some label in JanusGraph using Gremlin in Java. I tried the following:

public void setAllProperties(JanusGraphTransaction janusGraphTransaction) {
    GraphTraversal<Vertex, Vertex> traversal = janusGraphTransaction.traversal().V();
    traversal.has("SomeLabel", "SomeProperty", 0)
            .repeat(out("SomeEdgeLabel"))
            .property("SomeProperty", true)
            .until(outE("SomeEdgeLabel").count().is(0));
}

But no vertices are modified. I tried googling for modifying properties while traversing using repeat... until but without any success. Any suggestions?

stephen mallette · Accepted Answer · 2018-08-02T16:17:42.713

First, I think you need to iterate() your traversal - see tutorial - thus:

public void setAllProperties(JanusGraphTransaction janusGraphTransaction) {
    GraphTraversal<Vertex, Vertex> traversal = janusGraphTransaction.traversal().V();
    traversal.has("SomeLabel", "SomeProperty", 0)
            .repeat(out("SomeEdgeLabel"))
            .property("SomeProperty", true)
            .until(outE("SomeEdgeLabel").count().is(0)).iterate();
}

then, move the property() inside the repeat():

public void setAllProperties(JanusGraphTransaction janusGraphTransaction) {
    GraphTraversal<Vertex, Vertex> traversal = janusGraphTransaction.traversal().V();
    traversal.has("SomeLabel", "SomeProperty", 0)
            .repeat(out("SomeEdgeLabel").property("SomeProperty", true))
            .until(outE("SomeEdgeLabel").count().is(0)).iterate();
}

property() is not a type of Map step - it just passes the Vertex through so your traversal keeps working.

It works if I emit vertices then modify them in stream/list but the number of vertices will be extremely large - they won't fit into the memory. That's way I need to edit them while traversing. — Maciej Mościcki, Aug 02 '18 at 15:15
updated answer based on your comment. i think that's what you want anyway. i think you can drop the `until()` in this case as well — stephen mallette, Aug 02 '18 at 16:18

Modifying vertex properties while traversing

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