GraphTraversal works in Java but not in Python

[sharma-kunal]

I have a Janusgraph Server hosted on a machine and I want to traverse all the edges of a vertex.

I am using GraphTraversal in Java as shown below,

TypeSerializerRegistry typeSerializerRegistry = TypeSerializerRegistry.build()
                .addRegistry(JanusGraphIoRegistry.instance())
                .create();
Cluster cluster = Cluster.build()
    .addContactPoint("<Janus IP>")
    .serializer(new GraphBinaryMessageSerializerV1(typeSerializerRegistry))
    .port(8182)
    .create();

DriverRemoteConnection connection = DriverRemoteConnection.using(cluster, "g");
g = traversal().withRemote(connection);

GraphTraversal<Vertex, Map<Object, Object>> traversal = g.V().hasLabel("education").has("institute_name", "Mumbai University").inE().valueMap();
while (traversal.hasNext()) {
    Map<Object, Object> data = traversal.next();
    System.out.println(data.get("current_company"));
}

and it works fine, without any issues, now I want to do this in Python, but it is not working in Python, below is the code I am using in Python

connection = DriverRemoteConnection(url='ws://<Janus IP>:8182/gremlin', traversal_source='educationTestGraph')
g = traversal().withRemote(connection)

traversal = g.V().hasLabel("education").has("institute_name", "Mumbai University").inE().valueMap()
while traversal.hasNext():
    data = traversal.next()
    print(data.get("current_company"))

But it fails with the below error,

Received error message '{'requestId': '9ac8b34a-668b-445a-9966-4c4a0637994f', 'status': {'message': None, 'code': 500, 'attributes': {'stackTrace': 'java.lang.ClassCastException\n', 'exceptions': ['java.lang.ClassCastException']}}, 'result': {'data': None, 'meta': {}}}'
With results dictionary '{'9ac8b34a-668b-445a-9966-4c4a0637994f': <gremlin_python.driver.resultset.ResultSet object at 0x0000023F83391190>}'

[li-boxuan]

GraphBinary serializer doesn't work for python driver, as python driver is not natively supported by JanusGraph. That being said, it would work if you use GraphSON serializer on your server side:

{ className: org.apache.tinkerpop.gremlin.util.ser.GraphSONMessageSerializerV3, config: { ioRegistries: [org.janusgraph.graphdb.tinkerpop.JanusGraphIoRegistry] }}

[sharma-kunal]

I changed my serializer from

{ className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { ioRegistries: [org.janusgraph.graphdb.tinkerpop.JanusGraphIoRegistry] }}

to

{ className: org.apache.tinkerpop.gremlin.util.ser.GraphSONMessageSerializerV3, config: { ioRegistries: [org.janusgraph.graphdb.tinkerpop.JanusGraphIoRegistry] }}

in remote-objects.yaml file

Connecting to Janus from Python like below,

connection = DriverRemoteConnection(url='ws://<Janus IP>:8182/gremlin', traversal_source='educationGraph', message_serializer=serializer.GraphSONSerializersV3d0)

but, now it is failing with the below error

serialize_message() missing 1 required positional argument: 'request_message'

[li-boxuan]

You should add the serializer to the server side. Example: https://github.com/Citegraph/citegraph/blob/main/backend/src/main/resources/gremlin-server-cql.yaml

and then you could connect using python as follows:

from gremlin_python.process.anonymous_traversal import traversal
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
connection = DriverRemoteConnection("ws://localhost:8182/gremlin", "g")
g = traversal().withRemote(connection)