[jira] [Created] (TINKERPOP-2742) IO read may use wrong cardinality for property

["Boxuan Li (Jira)" <ji...@apache.org>]

Boxuan Li created TINKERPOP-2742:
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             Summary: IO read may use wrong cardinality for property
                 Key: TINKERPOP-2742
                 URL: https://issues.apache.org/jira/browse/TINKERPOP-2742
             Project: TinkerPop
          Issue Type: Bug
          Components: io
            Reporter: Boxuan Li


g.io(...).read() might lose list/set properties. See the example below:

gremlin> graph = TinkerGraph.open()
==>tinkergraph[vertices:0 edges:0]
gremlin> g = graph.traversal()
==>graphtraversalsource[tinkergraph[vertices:0 edges:0], standard]
gremlin> v1 = g.addV().property("feature0", "0.0").property("feature0", "1.1").next()
==>v[0]
gremlin> g.V().valueMap()
==>[feature0:[0.0,1.1]]
gremlin> g.io("graph.json").write().iterate()
gremlin> g.V().drop()
gremlin> g.io("graph.json").read().iterate()
gremlin> g.V().valueMap()
==>[feature0:[1.1]]

By verifying "graph.json", I am sure the write() step works fine. The problem is with read() step.

In [https://github.com/apache/tinkerpop/blob/5fdc7d3b5174f73475ca1a48920d5dec614ffc0e/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/util/Attachable.java#L294-L298,] it relies on the host graph to decide the cardinality for the given property key. In TinkerGraph, `features().vertex().getCardinality(anything)` always returns SINGLE, which means all vertex properties are created with SINGLE cardinality, even if the graph file itself contains multiple values for that property, as shown in the above case.

 

I presume TinkerGraph is not the only one who suffers from this problem. JanusGraph, if the default automatic schema maker is enabled, and a property wasn't defined explicitly, then SINGLE cardinality is returned by default. In this case, the loaded graph will be "wrong" in the sense that it turns LIST/SET values into a SINGLE value.



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