How to filter by count on gremlin map (OrientDB) - orientdb

Question

I have a somewhat similar business problem to - Gremlin filter by count
, but I'm running on OrientDB 3.0.16
This query:
g.V().hasLabel('skill').
groupCount()
Returns from OrientDB, as expected:
{
"result": [
{
"com": 1,
"netcompactframework": 1,
"netremoting": 2,
"netframework": 3,
"net": 1,
"netclr": 1
}
],
"elapsedMs": 18
}
I tried to apply an unfold and where filter after it:
g.V().hasLabel('skill').
groupCount().
unfold().
where(select(values).is(gt(1)))
But I get an error:
{
"errors": [
{
"reason": 501,
"code": 501,
"content": "java.lang.UnsupportedOperationException: Cannot convert netremoting=2 - class java.util.HashMap$Node to JSON"
}
]
}
It seems that problem is with unfold() as OrientDB is trying to convert the map entry string into JSON and fails
Any ideas?
Is this an OrientDB specific issue? Maybe there is another way to perform the same logic in gremlin?

Answer 1

That looks like a serialization error of some sort, but I'm not sure of the circumstance under which you are operating to get that problem. When you unfold() a Map, it gets converted to Java Map.Entry and returning that seems to be a problem for the serializer which along the way encounters the internal class HashMap$Node. I think you can work around this problem by folding back to a Map:
g.V().hasLabel('skill').
groupCount().
unfold().
where(select(values).is(gt(1))).
group().
by(keys).
by(select(values))
I would be curious to know what circumstances cause you to get that error. Standard GraphSON serializers in Gremlin Server should be able to handle HashMap$Node so it's curious that you'd be getting this problem at all.