Gremlin - Update or insert multiple vertices - gremlin

Question

I'm trying the following gremlin query to replace existing vertices if they exist but line V(__.select('id')).drop() keeps failing because __.select('id') does not return the id on that line.
vertices = [
{"id":1, "label": "person", "first_name":"bob","age":25,"height": 177},
{"id":2, "label": "person", "first_name":"joe","surname":"bloggs", "age": 32}
]
graph_traversal.inject(vertices).unfold().as_('entity'). \
V(__.select('id')).drop(). \
addV(__.select('label')).property(T.id, __.select('id')).as_('vertex'). \
sideEffect(__.select('entity').unfold().as_('kv').select('vertex'). \
property(
__.select('kv').by(Column.keys),
__.select('kv').by(Column.values)
)
)

Answer 1

Here is a way to approach it, but it requires that you do a bit of front end processing to your List of Map data to extract the "id" values so that they can be passed to g.V() directly.
gremlin> g = TinkerFactory.createModern().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
gremlin> data = [
......1> ["id":1, "label": "person", "first_name":"bob","age":25,"height": 177],
......2> ["id":2, "label": "person", "first_name":"joe","surname":"bloggs", "age": 32]
......3> ]
==>[id:1,label:person,first_name:bob,age:25,height:177]
==>[id:2,label:person,first_name:joe,surname:bloggs,age:32]
gremlin> g.V(data.collect{it.id}).
......1> sideEffect(drop()).
......2> fold().
......3> constant(data).
......4> unfold().as('properties').
......5> addV(select('label')).property(T.id, select('id')).as('vertex').
......6> sideEffect(select('properties').
......7> unfold().as('kv').
......8> where(select(keys).is(without('id','label'))).
......9> select('vertex').
.....10> property(select('kv').by(keys), select('kv').by(values)))
==>v[1]
==>v[2]
gremlin> g.V(1,2).elementMap()
==>[id:1,label:person,first_name:bob,age:25,height:177]
==>[id:2,label:person,surname:bloggs,first_name:joe,age:32]
Of particular note here is the use of fold() to reduce the stream of dropped vertex traversers to a single traverser (i.e. a List of those vertices) which then let's us replace that with a single instance of "data" to iterate over in the common fashion for using a Map to create a Vertex. Note that I added a where() to ignore the "id" and "label" keys since I figured you didn't want those values duplicated in as vertex properties.