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https://issues.apache.org/jira/browse/TINKERPOP3-924?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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pieter martin closed TINKERPOP3-924.
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Resolution: Fixed
Better described by [https://issues.apache.org/jira/browse/TINKERPOP3-968]
> Have an easier way to select full subgraphs/paths/trees
> -------------------------------------------------------
>
> Key: TINKERPOP3-924
> URL: https://issues.apache.org/jira/browse/TINKERPOP3-924
> Project: TinkerPop 3
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.1.0-incubating
> Reporter: pieter martin
> Assignee: Marko A. Rodriguez
>
> This issue follows on after some discussion on the gremlin users [mailing
> list | https://groups.google.com/forum/#!topic/gremlin-users/wziSPqeMxLg]
> where [~dkuppitz] has provided help.
> The requirement is to query a full subgraph from the graph. By full subgraph
> I mean that every element touched along the path is returned and not just the
> leaf elements at the n'th degree as is standard.
> The need to lift complete subgraphs is I think very common. Think of any tree
> structure, code or ui. It generally has leaf nodes at all sorts of depths.
> The other, is for any OGM tool to be able to eagerly hydrate an object graph
> with one gremlin query (optimized). This is something that if its supported
> greatly improves the usability and performance of the ORM tool.
> So at the ORM level or at pure gremlin its common usecase.
> Gremlin can do the above but not well. This requirement seeks an easier
> manner in which to return all friends and their addresses, in particular
> including friends that have no address.
> There is currently 2 ways in which gremlin already does return the full tree.
> As an simple example consider the following.
> {noformat}
> John--friend-->Peter--address-->NewYork
> --friend-->Joe
> --address-->Boston
> {noformat}
> I am looking for the full tree of john's friends and their addresses.
> It should return,
> {noformat}
> {John={Peter={NewYork}, Joe}}
> {noformat}
> h2. gremlin 1
> {noformat}
> g.V(person1).emit().repeat(out("friend", "address")).times(2).tree()
> {noformat}
> returns,
> {noformat}
> {John={Boston, Peter={NewYork}, Joe}}
> {noformat}
> This pattern is almost right but because "friend" and "address" is always
> traversed it returns John's address which is wrong for this use-case.
> This pattern is generally weak as just repeating all labels x times is
> inaccurate and fault prone and just plane semantically not what is required.
> The requirement is to specify the path exactly.
> h2. gremlin 2
> {noformat}
> g.V(john).choose(
> __.out("friend"), __.out("friend").choose(
> __.out("address"), __.out("address"), __.identity()
> ), __.identity()
> ).tree()
> {noformat}
> returns,
> {noformat}
> {John={Peter={NewYork}, Joe}}
> {noformat}
> This is correct and the path is specified exactly.
> But alas its a pain to construct, reads difficult and, at least in sqlg's
> case, very difficult to optimize.
> What I propose is direct support for returning a complete sub-graph.
> Something like, (only thinking about readability, not implementation here)
> {noformat}
> g.V(person1).emit(out("friend").out("address")).tree()
> or
> g.V(person1).emit().out("friend").out("address").tree()
> or
> g.V(person1).out("friend").out("address").fullTree()
> or
> g.V(person1).out("friend").out("address").completeTree()
> or
> g.V(person1).out("friend").out("address").subGraph()
> {noformat}
> Thanks
> Pieter
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