How do you find all vertices that have no incoming edges? - gremlin

Question

Below I'm trying to find all vertices where there are no incoming edges using a filter on the vertices. fullyQualifiedName is a unique index. I noticed some vertices that appeared to have incoming edges so I added a step below to just print them out if they existed. I would have expected no output since I thought I had filtered these vertices above; however, I'm still seeing incoming edges displayed.
def g = BerkeleyGraphFactory.create()
def vertices = g.V.filter {
it.inE('depends').count() == 0
}
Set<String> u = []
u.addAll(vertices.collect {v->
v.fullyQualifiedName
})
u.each {
def focusIter = g.V('fullyQualifiedName', it)
def vertex = focusIter.next()
// this shouldn't print out anything since these vertices were filtered above
vertex.inE('depends').each { e->
def classRefV = e.outV.next()
println it + " is used by " + classRefV.name + " " + e.toString()
}
}

Answer 1

I can't seem to recreate your problem. A rough simplification of your code here seems to show that things work as expected:
gremlin> g = TinkerGraphFactory.createTinkerGraph()
==>tinkergraph[vertices:6 edges:6]
gremlin> ids = g.V.filter{!it.inE('knows').hasNext()}.id.toList()
==>1
==>3
==>5
==>6
gremlin> ids.collect{g.v(it).inE('knows').toList()}
==>[]
==>[]
==>[]
==>[]
Perhaps you can try to convert your code to match the approach I took to see if that helps? I'm not sure what else to say short of you providing some sample data to work with for your specific case where the problem can be recreated.