Selecting a single value from a map

[Robert Dale]

Trying to use a value from a traversal induced map.

Many things are possible to select from (or do to) a map, but the ability to select single value by key seems to be absent.

{code}

g = TinkerGraph.open().traversal()

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').select(keys)

==>[name,age]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').select(values)

==>[marko,100]

gremlin> g.inject(['name':'marko','age':100]).as('a').select(first,'a')

==>[name:marko,age:100]

gremlin> g.inject(['name':'marko','age':100]).as('a').select(last,'a')

==>[name:marko,age:100]

gremlin> g.inject(['name':'marko','age':100]).as('a').select(all,'a')

==>[[name:marko,age:100]]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').map(values('name'))

java.util.LinkedHashMap cannot be cast to org.apache.tinkerpop.gremlin.structure.Element

Type ':help' or ':h' for help.

Display stack trace? [yN]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').values('name')

java.util.LinkedHashMap cannot be cast to org.apache.tinkerpop.gremlin.structure.Element

Type ':help' or ':h' for help.

Display stack trace? [yN]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').by(values('name'))

java.util.LinkedHashMap cannot be cast to org.apache.tinkerpop.gremlin.structure.Element

Type ':help' or ':h' for help.

Display stack trace? [yN]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').by('name')

java.util.LinkedHashMap cannot be cast to org.apache.tinkerpop.gremlin.structure.Element

Type ':help' or ':h' for help.

Display stack trace? [yN]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').order().by(keys)

==>[name:marko,age:100]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').order().by(values)

==>[name:marko,age:100]

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').range(local,0,1)

==>[name:marko]

{code}

Seems like by() and/or values() should be able to figure out it's taking a map and select that key.

Am I missing something or should I create a ticket?

Robert Dale

[Stephen Mallette]

I'm not sure if I've run into that specific issue before, but I've had problems with map manipulation too (not sure if there is a trick to solving your problems). As a larger issue, if we want to push users towards selecting just the data they want (as opposed to returning an entire Vertex/Edge) we probably need to be sure that Gremlin can work seamlessly with maps.

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[Robert Dale]

Figured it out by accident. It appears that select() actually does check the traversal for a map first and if it exists, selects that key. Otherwise, select will pick the labelled step.  Thus,

gremlin> g.inject(['name':'marko','age':100]).select('name')

==>marko

gremlin> g.inject(['name':'marko','age':100]).as('name').select('name')

==>marko

gremlin> g.inject(['name':'marko','age':100]).as('a').select('a').select('name')

==>marko

gremlin> g.inject(['name':'marko','age':100]).as('a').select('name')

==>marko

Ultimately, this now works:

g.inject(['name':'marko','age':100]).as('a').addV('person').property('name', select('a').select('name')).property('age',select('a').select('age'))

Robert Dale

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[Stephen Mallette]

good....i wish I'd better tracked some of my problems working with maps. i plan to pay more attention going forward given HaltedTraverserStrategy/Reference stuff.

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