Transactions in Tinkerpop3 DSE - gremlin

Question

This is a question to understand the transaction semantics in DSE graph via TinkerPop3 Java API
As I understand, when you have DseSession.executeGraph(String query) is executed in a single transaction.
But what is the mechanism to achieve the same using TinkerPop3 Java API ?
Say I want to add a vertex and then drop a few edges and then add a new vertex etc.,
I tried
g.V("{~label=company, id=12345}").drop().addV("company").property("id", "1").next()
This didn't work as I intended. (Dropping the company and adding one in a single transaction). The first vertex did indeed get deleted, however the new company was never created.
I got below exception
Exception in thread "main" java.util.NoSuchElementException
at com.datastax.dse.graph.internal.DseRemoteTraversal.nextTraverser(DseRemoteTraversal.java:60)

Answer 1

The drop() step "kills" the traverser you are deleting, meaning nothing is returned from drop(). You can see that if you try this:
gremlin> g.V().has('name','marko').drop().next()
java.util.NoSuchElementException
Type ':help' or ':h' for help.
Display stack trace? [yN]
Without a traverser there is nothing to feed forward to your addV() step that follows. There might be a nicer way to do this, but you can work around that problem by using inject() to add a throwaway value as a traverser that will feed into your addV(). In this case, you deleted one thing, so you need to put one traverser back to trigger the single call to addV() thus:
gremlin> g.V().has('name','marko').drop().
......1> inject(1).
......2> addV('person').property('name','stephen').next()
==>v[13]
I also wonder if this is a nice way to do it:
gremlin> g.V().has('name','marko').
......1> union(drop(),
......2> addV('person').property('name','stephen'))
==>v[13]