CODEWITHSUNDEEP
javaneo4jclient-servergremlintinkerpop3
rvw
rvw

Reputation: 125

TP3: Gremlin traversal and adding edges remotely with Java client

I would like to know if there is an easy way of adding edges to a remote graph from within a Java program. Currently, I have:

As far as I know, the Java application can only communicate with the server by submitting Gremlin queries through the client.submitAsync() method (right?).

My problem is as follows: I'd to look up two vertices, and if they both exist, create an edge between them. If the Graph object itself were available in my Java application, this would have been just as easy as it is in a local Gremlin console. I'd simply write the Java equivalent to

gremlin> v = g.addVertex('name', 'Hank')
==>v[16]
gremlin> v2 = g.addVertex('name', 'Pete')
==>v[18]
gremlin> v.addEdge('knows', v2)
==>e[20][16-knows->18]
gremlin>

Adding an edge to a graph on a remote server is more difficult as I need to find the two vertices first, before adding the edge between them. My Java code to do so is as follows:

//The params object is a Map that binds `fromParam` and `toParam` to strings Hank and Pete, respectively
ResultSet r = client.submitAsync("g.V().has('name', fromParam)", params).get();
ResultSet r2 = client.submitAsync("g.V().has('name', toParam)", params).get();

This gives me back two DetachedVertex objects. A third query to add an edge between them is then

// outVertex and inVertex are the DetachedVertex objects added to params
ResultSet r3 = client.submitAsync("outVertex.attach(g).addEdge('knows', inVertex.attach(g))", params).get();

This seems to work, but it had me stumped for a couple of hours and seems to be an enormous trouble for such an elementary operation. My questions are therefore as follows:

Upvotes: 2

Views: 1153

Answers (1)

Daniel Kuppitz
Daniel Kuppitz

Reputation: 10904

Can't you submit a multi-line statement? I've never tried that, but I'd say it should work.

However, we're currently working on steps to make that easier, but for now you can also do this (in case you need a one-liner):

g.V().has('name', fromParam).as('from').map {
    g.V().has('name', toParam).tryNext().orElse(false)
}.is(neq, false).addInE('knows', 'from')

The following example show how this approach performs for existing and non-existing vertices:

gremlin> g = TinkerFactory.createModern()
==>tinkergraph[vertices:6 edges:6]
gremlin> g.V().has("name","marko").out("created")
==>v[3]
gremlin> g.V().has("name","marko").as("from").map {
             g.V().has("name", "riple").tryNext().orElse(false)
         }.is(neq, false).addInE("created", "from") // riple doesn't exist, hence no edge is being created
gremlin> g.V().has("name","marko").out("created")
==>v[3]
gremlin> g.V().has("name","marko").as("from").map {
             g.V().has("name", "ripple").tryNext().orElse(false)
         }.is(neq, false).addInE("created", "from") // ripple does exist, hence a new edge is being created
==>v[5]
gremlin> g.V().has("name","marko").out("created")
==>v[3]
==>v[5]

Upvotes: 3

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