[TINKERPOP-792] select at start of match traversal on Map can fail

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.0.0-incubating
• Fix Version/s: 3.0.1-incubating, 3.1.0-incubating
• Component/s: process
• Assignee: Marko A. Rodriguez
• Reporter: Matt Frantz
• Created: 01/Aug/15 16:02
• Updated: 01/Sep/15 13:45
• Resolved: 01/Sep/15 13:45

Description

g.V().valueMap()
  .match(__.as('a').select('name').as('name'))
  .select('name')
The provided match pattern is unsolvable: [[MatchStartStep(a), SelectOneStep(name), MatchEndStep(name)]]

What I think it happening is that the select inside the match is using Scope.GLOBAL. The workaround is to insert identity, but I'm not sure why this works, as identity steps appear to be removed by strategy.

g.V().valueMap()
  .match(__.as('a').identity().select('name').as('name'))
  .select('name')
==>[marko]
==>[vadas]
==>[lop]
==>[josh]
==>[ripple]
==>[peter]