when selecting vertex using has('prop', 'value') with injected 'value' - graph-databases

Question

Is it possible to select vertex properties using injected values?
I can't use lambda that provided in the official doc: http://tinkerpop.apache.org/docs/current/reference/#inject-step since the lambda is not supported in our case.
I tried doing
g.inject('vadas').as('a').V().has('name', select('a'))
but it's returning all the vertices that have attribute 'name', seems like it's not selecting the injected value
Are there any ways I can do the 'has' filter based on some injected values?

Answer 1

Your query is supposed to return all vertices that have a name property, as select('a') should always return a value.
There is no way to use injected values and at the same time benefit from an index lookup. The only thing you can do is a full vertex scan:
gremlin> g.inject('vadas').as('a').V().where(eq('a')).by('name').by()
==>v[2]
That works well on a small in-memory graph, but it surely isn't a scalable solution.
UPDATE
If nested select()'s are not available, you could still do something like this:
gremlin> g = TinkerFactory.createModern().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
gremlin> data = ["marko": ["title": "dr", "age": 40]]
==>marko={title=dr, age=40}
gremlin> g.V().has("person","name",within(data.keySet())).as("v").
flatMap(constant(data).unfold().
where(eq("v")).
by(keys).
by("name").
select(values).
unfold()).as("kv").
select("v").
property(select("kv").by(keys), select("kv").by(values)).
iterate()
gremlin>
gremlin> g.V().valueMap()
==>[name:[marko],title:[dr],age:[40]]
...
There is a full scan in this traversal, but only over the data memory structure. Hence, if data isn't crazy large, the traversal performance should/could be acceptable.

Answer 2

#Daniel Kuppitz and #Huimin Yang, we have supported this feature, use property index scan, I think it will provide a useful ability
gremlin> g.inject('vadas').as('a').V().has('name', eq(select('a'))).profile()
==>Traversal Metrics
Step Count Traversers Time (ms) % Dur
=============================================================================================================
InjectStep([vadas])#[a] 1 1 0.090 0.51
GraphDbGraphStep(vertex,[name.eq([SelectOneStep... 1 1 17.768 99.49
>TOTAL - - 17.859 -
gremlin> g.inject('vadas').as('a').V().has('name', eq(select('a')))
==>v[vadas]