Azure Cosmos Graph nest edge vertex in a vertex property

Question

I have two vertex:

1) Vertex 1: { id: 1, name: “john” }

2) Vertex 2: { id: 2, name: “mary” }

There is an edge from 1 to 2 named “children”.

Is it possible to return 2 nested in 1 using gremlin like this?

  { 
    id: 1, 
    name: “john”,
    children: { id: 2, name: “mary” }
  }

Thank you!

My solution with an amazing help of @noam621 ---------------------------------


g.V(1)
.union( valueMap(true),
        project('children').by( coalesce( out('children').valueMap(true).fold() , constant([]))),
        project('parents').by( coalesce( out('parents').valueMap(true).fold() , constant([])))
)
.unfold().group().by(keys).by(select(values))

It returns the following object:

{ 
    id: 1, 
    name: [ “john” ],
    children: [ { id: 2, name: [ “mary” ] } ],
    parents: []
}

.union with project are the key to merge all objects in one object. valueMap(true).fold() is fundamental to get all objects in the edge and coalesce helps with a default value if the edge doesn't return any vertex.

Due to some Azure Cosmos gremlin limitations is only possible to get values as array values. Thus I finalized the object formatting in my application code. It's ok for now.

Thank you!

noam621 · Accepted Answer · 2020-04-06T07:21:01.390

2

You can do it by using the project step for both vertexes:

g.V(1).project('id', 'name', 'children').
    by(id).
    by('name').
    by(out('children').
      project('id', 'name').by(id).
        by('name'))

example: https://gremlify.com/3j

query with valueMap:

g.V(1).union(
    valueMap().
      with(WithOptions.tokens).by(unfold()),
    project('children').
      by(out('children').
        valueMap().
          with(WithOptions.tokens).by(unfold()))
  ).unfold().
  group().by(keys).
    by(select(values))

if valueMap().with(WithOptions.tokens) not supported in Cosmos use valueMap(true) instead

edited Apr 06 '20 at 07:21

answered Apr 05 '20 at 07:50

noam621

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5

it's always better to prefer token based `by()` modulators, thus prefer `by(id)` to `by(id())` and `by("name")` to `by(values('name'))` - https://tinkerpop.apache.org/docs/current/recipes/#steps-instead-of-tokens – stephen mallette Apr 05 '20 at 10:51
1

Great!!! It works very well! :D Just one more question on this, is it possible to project to all properties instead of specifying each one? Thanks!! – Murilo Maciel Curti Apr 05 '20 at 16:50
1

@MuriloMacielCurti You can use `elementMap` or `valueMap` and then merge it with `project` only for the 'children' field. look here on merging maps: https://stackoverflow.com/questions/60307292/merging-maps-in-gremlin – noam621 Apr 05 '20 at 21:01
@noam621 I'm going to test here and I will return with the results. Thank you so much! – Murilo Maciel Curti Apr 06 '20 at 00:43
@noam621 I couldn't figure out how to achieve this. Can you share an example pls? I think elementMap is not available on Azure Cosmos Db. Thank you – Murilo Maciel Curti Apr 06 '20 at 01:45
@MuriloMacielCurti look at the new query I added – noam621 Apr 06 '20 at 07:21
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/211061/discussion-between-murilo-maciel-curti-and-noam621). – Murilo Maciel Curti Apr 06 '20 at 11:31

Azure Cosmos Graph nest edge vertex in a vertex property

1 Answers1