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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