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https://issues.apache.org/jira/browse/TINKERPOP-2742?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephen Mallette reopened TINKERPOP-2742:
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> 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
> Assignee: Stephen Mallette
> Priority: Major
> Fix For: 3.7.0
>
>
> g.io(...).read() might lose list/set properties. See the example below:
> {noformat}
> 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]]{noformat}
> 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 default cardinality SINGLE (unless otherwise configured), 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. For
> example, for 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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