JanusGraph中的Date属性的min()

Question

在JanusGraph中,我想获得一些Date属性的min().

由于min()和max()都只支持Numbertype,我使用map{it.get().getTime()}.但奇怪的结果.

怎么做 ？

• JanusGraph版本:github master(大约2周前建立)
• Gremlin版本:3.2.6

架构定义

gremlin> mgmt = graph.openManagement()
==>org.janusgraph.graphdb.database.management.ManagementSystem@496a8a94

gremlin> person = mgmt.makeVertexLabel('Person').make()
==>Person

gremlin> t_created = mgmt.makePropertyKey('t_created').dataType(Date.class).cardinality(SINGLE).make()
==>t_created

gremlin> t_modified = mgmt.makePropertyKey('t_modified').dataType(Date.class).cardinality(SINGLE).make()
==>t_modified

gremlin> mgmt.buildIndex('i_t_created', Vertex.class).addKey(t_created).buildMixedIndex('search')
==>i_t_created

gremlin> mgmt.buildIndex('i_t_modified', Vertex.class).addKey(t_modified).buildMixedIndex('search')
==>i_t_modified

gremlin> mgmt.commit()
==>null

我的gremlin控制台代码

gremlin> person = g.addV('Person').property('t_created', new Date()).property('t_modified', new Date()).next()
==>v[16488]

gremlin> g.tx().commit()
==>null

gremlin> g.V(person).properties()
==>vp[t_created->Tue Sep 05 07:40:16 ]
==>vp[t_modified->Tue Sep 05 07:40:16 ]

gremlin> g.V(person).values('t_created', 't_modified')
==>Tue Sep 05 07:40:16 UTC 2017
==>Tue Sep 05 07:40:16 UTC 2017

gremlin> g.V(person).values('t_created', 't_modified').min()
java.util.Date cannot be cast to java.lang.Number
Type ':help' or ':h' for help.
Display stack trace? [yN]

gremlin> g.V(person).values('t_created', 't_modified').map{it.get().getTime()}
==>1504597216099
==>1504597216099

// max() is OK
gremlin> g.V(person).values('t_created', 't_modified').map{it.get().getTime()}.max()
==>1504597216099

// Why min() is 2147483647 ?
gremlin> g.V(person).values('t_created', 't_modified').map{it.get().getTime()}.min()
==>2147483647

Answer 1

我不知道为什么你会得到2147483647,但是你可以试试其他的东西:

gremlin> g.addV().property("foo", new Date())
==>v[0]
gremlin> g.addV().property("foo", new Date())
==>v[2]
gremlin> g.V().values("foo")
==>Tue Sep 05 07:02:15 MST 2017
==>Tue Sep 05 07:02:18 MST 2017
gremlin> g.V().values("foo").order().by().limit(1)     // min()
==>Tue Sep 05 07:02:15 MST 2017
gremlin> g.V().values("foo").order().by(decr).limit(1) // max()
==>Tue Sep 05 07:02:18 MST 2017

这种方法的好处是,它不需要lambda步骤.