Hi,
Matt Frantz had this idea the other day:
https://issues.apache.org/jira/browse/TINKERPOP3-652
I was anti it at first cause then match() looks like this:
g.V.match(…).select(local,'a','b')
Gross… However, it makes sense as select() was too overloaded with both global
analysis (Path) and local analysis (Map<String,Object>). To rectify the
ugliness of select(local,'a','b'), I made an interface called Scoping which
allows a step to recommend a Scope. Thus, MatchStep's recommend scope is
Scope.local. There is a ScopingStrategy that then uses scope recommendations.
https://github.com/apache/incubator-tinkerpop/blob/master/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/strategy/finalization/ScopingStrategy.java
So, now we are back to:
g.V.match(…).select('a','b')
So thats good. However, check out what you can do now that both select() and
where() can be scoped.
gremlin> g = TinkerFactory.createModern().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:6], standard]
gremlin> // no except() needed any more! thats huge. i have always hated
except/retain and now they can go away.
gremlin>
g.V(1).as('a').out('created').in('created').as('b').where('a',neq('b')).values('name')
==>josh
==>peter
gremlin>
g.V(1).as('a').out('created').in('created').as('b').where('a',neq('b')).select().by('name')
==>[a:marko, b:josh]
==>[a:marko, b:peter]
gremlin>
g.V(1).as('a').out('created').in('created').as('b').select().by('name').where('a',neq('b'))
==>[a:marko, b:josh]
==>[a:marko, b:peter]
…where() can operate on current object Maps or it can operate on global Paths
(similar to select()). The last two examples are crazy cause of ScopeStrategy.
Check the toString():
gremlin>
g.V(1).as('a').out('created').in('created').as('b').where('a',neq('b')).select().by('name').iterate().toString()
==>[TinkerGraphStep([1],vertex)@[a], VertexStep(OUT,[created],vertex),
VertexStep(IN,[created],vertex)@[b], WhereStep(global,a,neq,b),
SelectStep(global,[value(name)])]
gremlin>
g.V(1).as('a').out('created').in('created').as('b').select().by('name').where('a',neq('b')).iterate().toString()
==>[TinkerGraphStep([1],vertex)@[a], VertexStep(OUT,[created],vertex),
VertexStep(IN,[created],vertex)@[b], SelectStep(global,[value(name)]),
WhereStep(local,a,neq,b)]
Notice in the second example how the WhereStep uses local. Why? Cause
SelectStep projects down to a Map. No need to do double path analysis. Neato.
Enjoy,
Marko.
http://markorodriguez.com
