[TINKERPOP-2314] Employ by(String) for Map when possible and improve errors around incorrect types

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Done
• Affects Version/s: 3.3.9
• Fix Version/s: 3.5.0, 3.4.5
• Component/s: process
• Assignee: Stephen Mallette
• Reporter: Stephen Mallette
• Created: 13/Nov/19 19:08
• Updated: 26/Nov/19 12:00
• Resolved: 26/Nov/19 12:00

Description

This bit of Gremlin demonstrates both problems for uses of by(String):

gremlin> g.V().valueMap().project('x').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]n

First, users typically expect this to work because they figure they are just grabbing a keys value from a Map and then get the difficult to understand message which doesn't tell you how to resolve. As a side note, the way to resolve is with:

gremlin> g.V().valueMap().project('x').by(select('name'))
==>[x:[marko]]
==>[x:[stephen]]
==>[x:[matthias]]
==>[x:[daniel]]
==>[x:[gremlin]]
==>[x:[tinkergraph]]

Issue Links

• links to: GitHub Pull Request #1223