Gremlin drop deletes only the first vertex of the sub-graph

Question

I have a graph where A is connected to B,C,D with edges.
I'm using the following to delete A and its connected vertexes.

g.V('A').
  union(__(),
    repeat(out()).emit()).drop()

But it deletes only A.
When I run it without the drop() it returns a list of all the sub-graph vertexes.
I'm using the tinkerpop console/server version 3.4.9.

Answer 1

You need to collect the results of the union step before calling drop. Here is the query slightly modified.

gremlin> g.addV('A').as('a').
......1>   addV('B').as('b').
......2>   addV('C').as('c').
......3>   addV('D').as('d').
......4>   addE('knows').from('a').to('b').
......5>   addE('knows').from('b').to('c').
......6>   addE('knows').from('c').to('d') 
==>e[41][37-knows->38]


gremlin>   g.V().hasLabel('A').
......1>   union(identity(),
......2>     repeat(out()).emit()).fold() 
==>[v[35],v[36],v[37],v[38]]


gremlin>   g.V().hasLabel('A').
......1>   union(identity(),
......2>     repeat(out()).emit()).fold().unfold().drop()   

gremlin> g

==>graphtraversalsource[tinkergraph[vertices:0 edges:0], standard]

Note also that this can be done without the need for a union step by moving the emit before the repeat and using store.

g.V().hasLabel('A').
  emit().
  repeat(store('v').out()).
  cap('v').
  unfold().
  drop()