Could not locate method: DefaultGraphTraversal.to with neo4j plugin and gremlin server

Question

I am using the gremlin plugin for nodejs, communicating to gremlin server with an embedded neo4j graph. I am able to query and create vertices, but unable to create any edges due to an error "Could not locate method: DefaultGraphTraversal.to." Any ideas??

I am able to create vertices and edges using the gremlin console connecting to the same gremlin server as the nodejs program.

Gremlin console & server 3.4.1 Gremlin NodeJS npm 3.4.1 Tinkerpop Neo4J-gremlin plugin: 3.4.1

const gremlin = require('gremlin');
const traversal = gremlin.process.AnonymousTraversalSource.traversal;
const Graph = gremlin.structure.Graph;
const DriverRemoteConnection = gremlin.driver.DriverRemoteConnection;

const g = traversal().withRemote(new DriverRemoteConnection('ws://localhost:8182/gremlin'));

async function run(){

    const phil = await g.V().has('name', 'phil').next();
    console.log("Have Phil: " +JSON.stringify(phil ));

    g.V().has('name', 'stephen').next()
    .then(stephen => {
        console.log("Have Steve: " +JSON.stringify(stephen));
        const e1 = g.V(phil).addE('friends').to(stephen).next();
        console.log(e1);
    })
    .catch(err => console.log(err));

}

run();

Below is the output. As you can see, I am able to fetch the vertices fine, but receive this error during the edge creation.

Have Phil: {"value":{"id":18,"label":"person"},"done":false}
gremlin.js:13
Have Steve: {"value":{"id":7,"label":"person"},"done":false}
gremlin.js:17
Promise { pending }
gremlin.js:19
(node:48830) UnhandledPromiseRejectionWarning: Error: Server error: Could not locate method: DefaultGraphTraversal.to([{value={id=7, label=person}, done=false}]) (599)
    at Connection._handleMessage (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/gremlin/lib/driver/connection.js:265:9)
    at WebSocket._ws.on (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/gremlin/lib/driver/connection.js:128:43)
    at WebSocket.emit (events.js:189:13)
    at Receiver._receiver.onmessage (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/ws/lib/WebSocket.js:141:47)
    at Receiver.dataMessage (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/ws/lib/Receiver.js:380:14)
    at Receiver.getData (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/ws/lib/Receiver.js:330:12)
    at Receiver.startLoop (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/ws/lib/Receiver.js:165:16)
    at Receiver.add (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/ws/lib/Receiver.js:139:10)
    at Socket._ultron.on (/Users/byronbailey/OneDrive - Cargill Inc/VSC/GraphTest/node_modules/ws/lib/WebSocket.js:138:22)
    at Socket.emit (events.js:189:13)
warning.js:18
(node:48830) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
warning.js:18
(node:48830) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

B Bailey B Bailey · Accepted Answer · 2019-05-22T08:31:27

The problem was the data type of the parameters. I had tried different versions of this solution before, but evidently still missed the mark. The addE line of code should be as shown below. This Azure sample helped connect the dots.

g.V(phil.value.id).addE('knows').to(g.V(stephen.value.id)).next()

Could not locate method: DefaultGraphTraversal.to with neo4j plugin and gremlin server

1 Answers