stephen mallette commented on TINKERPOP-1463:

I'll let [~dkuppitz] say otherwise/more, but I understood that we were doing 

> It would make more sense if the filter-traversal would at least start from 
> the property, not from the value. Then we could use it to filter vertices 
> based on meta-properties.

> Will these automagically become index lookups or will the vendor have to 
> implement something?

I don't think those will turn into index lookups automatically because that 
overload of {{has()}} will use {{TraversalFilterStep}} and I'm guessing that 
most graph systems won't fold that up with their strategies.

> Improve has(propertyKey, traversal)
> -----------------------------------
>                 Key: TINKERPOP-1463
>                 URL: https://issues.apache.org/jira/browse/TINKERPOP-1463
>             Project: TinkerPop
>          Issue Type: Improvement
>          Components: process
>    Affects Versions: 3.2.5
>            Reporter: Daniel Kuppitz
>            Priority: Major
> Two issues here:
> {{.has(propertyKey, traversal)}} kinda doesn't work as expected:
> {code}
> gremlin> g = TinkerFactory.createModern().traversal()
> ==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
> gremlin> g.addV(label, "software",  "lang", "python")
> ==>v[12]
> gremlin> g.V().has("name","lop").values("lang").as("l").V().has("lang", 
> select("l"))
> ==>v[3]
> ==>v[5]
> ==>v[12]
> gremlin> g.V().has("name","lop").values("lang").as("l").V().has("lang", 
> __.where(eq("l")))
> ==>v[3]
> ==>v[5]
> {code}
> From a user perspective {{.has("lang", select("l"))}} is / would be 
> self-explanatory, {{.has("lang", __.where(eq("l")))}} on the other hand is 
> confusing and I don't see good use-cases for it, as you could also write:
> {code}
> g.V().has("name","lop").values("lang").as("l").V().where(values("lang").as("l"))
> {code}
> The second issue or follow-up issue is, that has-traversal should be folded 
> into the {{GraphStep}}, so that the mid-traversal {{V()}} is not a full graph 
> scan. Given the traversal:
> {code}
> g.V().has("name","lop").values("lang").as("l").V().has("lang", select("l"))
> {code}
> ... we would know the value of {{"l"}} at runtime. Thus it's not much 
> different from
> {code}
> g.V().has("name","lop").values("lang").as("l").V().has("lang", "java")
> {code}
> The only difference is that the latter traversal knows that the {{lang}} 
> value is {{java}} at compile time and the former traversal only knows it at 
> runtime. In either case the value is known before it's needed for the 
> mid-traversal {{V().has(...)}} lookup part.

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