Gremlin Python mergeV on match doesnt update properties

[Hugo Ferney Alvarez Lucena]

I'm working with gremlin python and AWS Neptune, and I'm trying to update vertex properties with MergeV step and option OnMatch, but instead of update the value, it looks like append the value on a list, someone know how to update vertex properties with merge?
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[Cole Greer]

Hi Hugo,

I believe your question has already been answered in the TinkerPop discord. Just to close the loop over here, what you are seeing is a result of Neptune using "set cardinality" for properties instead of "single". If you are using a database which supports TinkerPop 3.7.0 or newer, the correct syntax to specify single cardinality for a property is as follows:

from gremlin_python.process.traversal import Merge, T, CardinalityValue g.merge_v({T.id_: "x1234"}) .option(Merge.on_create, {T.label: 'Dog', 'name': 'Toby', 'age': 10}) .option(Merge.on_match, {'age': CardinalityValue.single(11)}) .toList()

If it is not possible to upgrade to a database which supports TinkerPop 3.7, then the following example should work. I generally wouldn't recommend using the following syntax unless necessary as it's effectively abusing the onMatch traversal to directly write the updated properties, instead of producing a property map as intended:

g.merge_v({T.id_: "x1234"}) .option(Merge.on_create, {T.label: 'Dog', 'name': 'Toby', 'age': 10}) .option(Merge.on_match, __.side_effect(__.property(Cardinality.single, "age", 11)).constant(dict())) .toList()

Cole Greer