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javacyphertinkerpoptinkerpop3

Match NOT in Tinkerpop traversal

I'd like to match all b1, where no node b2 exists as depicted below. enter image description here This is some kind of a 2-hop asymmetry. Note that the non-existent b2 must link to the same c:C as b1, so other (a2) --> (b3) --> (a1) can be ignored as long as b3 has no edge to c:C.

I tried the following...

graph.traversal().V()
    .match(
        as("c").hasLabel("C"),

        as("a").hasLabel("A")
        .out().hasLabel("B").as("b1")
        .where(out().as("c"))
        .out().hasLabel("A").as("a2"),

        not(
        as("a2")
        .out().hasLabel("B").as("b2")
        .where(out().as("c")
        .out().as("a1")
    )
)

...but second MATCH step throws an exception:

java.lang.IllegalStateException: The provided match pattern is unsolvable: [[MatchStartStep(a1), HasStep([~label.eq(A)]), VertexStep(OUT,vertex), HasStep([~label.eq(B)]), WhereTraversalStep([WhereStartStep, VertexStep(OUT,vertex), WhereEndStep(c)])@[b1], VertexStep(OUT,vertex), HasStep([~label.eq(A)]), MatchEndStep(a2)], [MatchStartStep(a2), HasStep([~label.eq(B)]), WhereTraversalStep([NotStep([WhereStartStep, VertexStep(OUT,edge)])]), WhereTraversalStep([WhereStartStep, VertexStep(OUT,vertex)@[c], VertexStep(OUT,vertex), WhereEndStep(a1)])@[b2], MatchEndStep, MatchEndStep]]

I can't even match this is Cypher, unfortunately.

Solution

  • Suddenly, I found a solution which avoids scope problems:

    graph.traversal().V()
    as("a").hasLabel("A")
    .out().hasLabel("B").as("b1")
    .where(out().hasLabel("C"))
    .out().hasLabel("A").as("a2")
    .where(
        not(
            out().hasLabel("B")
                .where(out().hasLabel("C"))
                .out().as("a")
        )
    )