How do I get all the edges, associated vertices, and the respective id, label and properties via gremlin-python?

Question

I want to fetch all the edges and associated vertices from my AWS Neptune DB. In addition, I want the id, labels and properties for the nodes as well as edges.
My data is a stored as a property graph and I'm using gremlin-python to query it.

Below is a query which provides the required data when executed in the gremlin shell. However, trying to execute the same using gremlin-python throws an error.

g.V().bothE().otherV().limit(2).path().by(__.valueMap(true))

Python variant

from gremlin_python import statics
from gremlin_python.structure.graph import Graph
from gremlin_python.process.traversal import T
from gremlin_python.process.graph_traversal import __
from gremlin_python.process.strategies import *
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection

# Define a graph instance
graph = Graph()

# Connect to the neptune instance
try:
    remoteConn = DriverRemoteConnection('wss://<YOUR_NEPTUNE_IP>:8182/gremlin', 'g')
    g = graph.traversal().withRemote(remoteConn)
except:
    print("Couldn't connect successfully with Neptune instance")
    exit()

g.V().bothE().otherV().limit(2).path().by(__.valueMap(True))

Error

GremlinServerError: 498: {"requestId":"...","code":"UnsupportedOperationException","detailedMessage":"org.apache.tinkerpop.gremlin.process.traversal.step.util.ImmutablePath cannot be cast to org.apache.tinkerpop.gremlin.structure.Element"}

Can someone provide me a way to get the required information? Be it by successfully converting the above query to Python or via some other query.

stephen mallette stephen mallette · Accepted Answer · 2019-07-19T14:05:39

Your traversal looks valid to me and in fact seems to work fine with TinkerGraph:

gremlin> g.V().bothE().otherV().limit(2).path().by(__.valueMap(true))
==>[[id:1,name:[marko],label:person,age:[29]],[id:9,weight:0.4,label:created],[id:3,name:[lop],lang:[java],label:software]]
==>[[id:1,name:[marko],label:person,age:[29]],[id:7,weight:0.5,label:knows],[id:2,name:[vadas],label:person,age:[27]]]

I would expect that to work. Perhaps that is a bug in Neptune? Note that you can get the same result by using select() but it is a bit more verbose:

gremlin> g.V().as('a').bothE().as('b').otherV().as('c').limit(2).select('a','b','c').by(valueMap(true))
==>[a:[id:1,name:[marko],label:person,age:[29]],b:[id:9,weight:0.4,label:created],c:[id:3,name:[lop],lang:[java],label:software]]
==>[a:[id:1,name:[marko],label:person,age:[29]],b:[id:7,weight:0.5,label:knows],c:[id:2,name:[vadas],label:person,age:[27]]]

You can of course unfold() the Map instances produced by select() to get the same output format as path()

gremlin> g.V().as('a').bothE().as('b').otherV().as('c').limit(2).select('a','b','c').by(valueMap(true)).map(unfold().select(values).fold())
==>[[id:1,name:[marko],label:person,age:[29]],[id:9,weight:0.4,label:created],[id:3,name:[lop],lang:[java],label:software]]
==>[[id:1,name:[marko],label:person,age:[29]],[id:7,weight:0.5,label:knows],[id:2,name:[vadas],label:person,age:[27]]]

How do I get all the edges, associated vertices, and the respective id, label and properties via gremlin-python?

1 Answers