Check whether a particular vertex exists or not in gremlin traversal

[Monel Gupta]

I am trying to check first that whether a particular Vertex Exists in a graph or not if, it doesn't exists then i am creating a new vertex, the checker is based on properties , Here is the following code :

    public Vertex addVertex(Enum label, Map properties){

Vertex x = null;int fl=0,f=0;

if(properties.size()==0)

return null;

GraphTraversalSource g = graph.traversal();

Set<Enum> keys = properties.keySet();

for(Enum key: keys){

f++;

       properties.get(key);

       System.out.println("enter");

       if(g.V().hasLabel(label.toString()).has(key.toString(),properties.get(key)).next()!=null  ){

       fl++;

       System.out.println("exit");

       x=  g.V().hasLabel(label.toString()).has(key.toString(),properties.get(key)).next();

       System.out.println("exit2");

       }

}

if(fl==f){

return x;

}

x=graph.addVertex(T.label,label.toString(),properties);

return x;

}

But i am getting the following error .

    Exception in thread "main" org.apache.tinkerpop.gremlin.process.traversal.util.FastNoSuchElementException

How can this be solved, any leads will be really appreciated

[Daniel Kuppitz]

Wow, you should really take your time and read the docs to learn what Gremlin can do what not. We could go through your code, but I don't think it's worth it.

public Vertex getOrCreateVertex(final GraphTraversalSource g, final Enum label, final Map<Enum, Object> properties) {

    if (properties == null || properties.size() == 0) {

        return null;

    }

    final String vlabel = label.toString();

    GraphTraversal<Vertex, Vertex> getter = g.V().hasLabel(vlabel);

    GraphTraversal<Vertex, Vertex> creator = g.addV(T.label, vlabel);

    for (final Enum key : properties.keySet()) {

        final String pkey = key.toString();

        final Object pval = properties.get(key);

        getter = getter.has(pkey, pval);

        creator = creator.property(pkey, pval);

    }

    final GraphTraversal<Vertex, Vertex> factory = creator; 

    return getter.tryNext().orElseGet(factory::next);

}

Seriously, please read the docs.

Cheers,

Daniel

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[Jason Plurad]

Quick inspection of your code...

if (g.V().hasLabel(label.toString()).has(key.toString(),properties.get(key)).next() != null)

This can throw a FastNoSuchElementException. The graph traversal is an Iterator, so you should check hasNext() instead of next() != null.