similar edges and how to prevent them

[yair...@gmail.com]

I have an app where I am migration a d non graph DB graph to Janus. So I create the graph when I first start the app. Using cassandra backend.

I have an issue where 2 vertices have "identical" edges (besides the auto-generated id of course) are created in my code causing me to get too many IN and OUT edges.

I read my vertex like this:

javaGraph.traversal().V().hasLabel(instanceId).has("nodeId", lineageNodeId).toList();

I read Both edges:

vertex.edges(org.apache.tinkerpop.gremlin.structure.Direction.IN, "link");


vertex.edges(org.apache.tinkerpop.gremlin.structure.Direction.OUT, "link");

each time I run my app it doesn't "see" the existing edges and adds to it. so I get edges multiplies while I only want "link" edge between any 2 given vertices

in order to make sure I don't create duplicate vertices:

        GraphTraversal<Vertex, Vertex> vertexNode = javaGraph.traversal().V().hasLabel(instanceId).has("nodeId", myNodeId);

        if (vertexNode.hasNext()) {

            return vertexNode.next();

        } else {            

            JanusGraphVertex node = javaGraph.addVertex(instanceId);

            node.property("nodeId", myNodeId);

            return node;

        }

But I don't know once I have vertex A and B at hand - how to verify they are not already connected.

[yair...@gmail.com]

One Option I thought of that should have worked but doesn't is:

Assuming I have a method to create between 'from' vertex and 'to' vertex:

        Iterator<Edge> edgesIter = from.edges(Direction.OUT, "link");


        while (edgesIter.hasNext()) {
            Edge edge = edgesIter.next();
            Vertex outVertex = edge.outVertex();
            if(outVertex.property("nodeId").value().equals(to.property("nodeId").value())){
                return edge;
            }


        }
        org.apache.tinkerpop.gremlin.structure.Edge linkedEdge = from.addEdge("link", to);
        return linkedEdge;

I still get duplicate edges when I re-run my app. and yes I do commit the tx after i'm done.

Any ideas?

[tpr...@gmail.com]

You can use coalesce step to do a check or insert query.
http://tinkerpop.apache.org/docs/current/reference/#coalesce-step
Something like g.V(idTo).as('to').V(idFrom).coalesce(__.outE('labelE').has('id',idValue),
__.addE('labelE').property('id',idvalue).to('to'))

[Daniel Kuppitz]

I guess the point is, that the edge's direction doesn't matter. Hence it should be more like:

g.V().has(instanceId, "nodeId", nodeA).as("a").

  V().has(instanceId, "nodeId", nodeB).

  coalesce(bothE("link").where(otherV().as("a")),

           addE("link").to("a"))

...or, if performance matters, don't enable path computations (using otherV):

g.V().has(instanceId, "nodeId", nodeA).as("a").

  V().has(instanceId, "nodeId", nodeB).

  coalesce(outE("link").where(inV().as("a")),

           inE("link").where(outV().as("a")),

           addE("link").to("a"))

Cheers,

Daniel

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[than...@gmail.com]

Hi Daniel,

I want to create both vertex and edge if they are not exist. 

I do as the following but it's not work (vertices have been created but no relation between them)

g.V().hasLabel("V1")
.has("userId", userId).fold()
.coalesce(
        unfold(),
        addV("V1").property("userId", userId1)
).as("a")
.V().hasLabel("V1").has("userId", userId2).fold()
.coalesce(
        unfold(),
        addV("V1").property("userId", userId2)
)
.coalesce(
        bothE("link").where(outV().as("a")),
        addE("link").from("a")
)

Do you know why?

Vào 20:37:18 UTC+7 Thứ Hai, ngày 11 tháng 9 năm 2017, Daniel Kuppitz đã viết:

I guess the point is, that the edge's direction doesn't matter. Hence it should be more like:

g.V().has(instanceId, "nodeId", nodeA).as("a").

  V().has(instanceId, "nodeId", nodeB).

  coalesce(bothE("link").where(otherV().as("a")),

           addE("link").to("a"))

...or, if performance matters, don't enable path computations (using otherV):

g.V().has(instanceId, "nodeId", nodeA).as("a").

  V().has(instanceId, "nodeId", nodeB).

  coalesce(outE("link").where(inV().as("a")),

           inE("link").where(outV().as("a")),

           addE("link").to("a"))

Cheers,

Daniel

On Mon, Sep 11, 2017 at 3:32 AM, <tpr...@gmail.com> wrote:

You can use coalesce step to do a check or insert query.
http://tinkerpop.apache.org/docs/current/reference/#coalesce-step
Something like g.V(idTo).as('to').V(idFrom).coalesce(__.outE('labelE').has('id',idValue),
     __.addE('labelE').property('id',idvalue).to('to'))

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[Daniel Kuppitz]

There are two issues in your query. The first one is the reason why it doesn't work as expected: the fold() step. Using fold() will destroy the path history, but you can easily work around it, by doing that part in a child traversal:

g.V().has("V1","userId", userId).fold().

  coalesce(unfold(),

           addV("V1").property("userId", userId1)).as("a").

  map(V().has("V1","userId", userId2).fold()).

  coalesce(unfold(),

           addV("V1").property("userId", userId2))

  coalesce(bothE("link").where(outV().as("a")),

           addE("link").from("a"))

The second issue is the combination of bothE and outV. You should rather use bothE/otherV, outE/inV or inE/outV.

Cheers,

Daniel

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