gremlin traversal on AWS neptune

Question

I have a graph structure like this-

Node1(Console)   <----Uses---  Node2(Name, Age) -----plays----> Node3(Game)
 

So, i have three nodes -

Node1 is console like a PS3/ Nintendo.

Node2 is a person with properties name and Age.

Node3 is game node which holds game name like 'warcraft'.

Now I want to have a gremlin query which tells me that. How many users (Node2) who has the console like PS3, plays a game like 'warcraft'

I think i need to start the traverse from Node2 , filter it based on Node1 property i.e console as as 'PS3' and plays game like 'warcraft'

I am new to gremlin and using some thing like this -

g.V().hasLabel('user').outE('uses').inV().has('console', 'ps3').count()

the above query only answers half of my required result. How do i filter Node2 based on plays relationship as well.

Any help is appreciated.

Answer 1

There are multiple ways to write the query.

Option 1: Start from console

g.V().has('console', 'ps3').in('uses').where(out('plays').has('game', 'warcraft')).valueMap('name')

Let me explain the structure here:

g.V().has('console', 'ps3') --> Select all vertices which have a property with key as console and value as ps3

in('uses') --> From the set of previous vertices, jump to incoming vertices via an edge that has the label uses. At this stage, we would have player vertices in our solution.

where(out('plays').has('game', 'warcraft')) --> Apply a filter on existing solutions. Since we are using where we would not jump/traverse to the next step of vertices.

valueMap('name') --> Project one or more properties if existing solutions which are player vertices.

Option 2: Another way to write above query

g.V().has('console', 'ps3').in('uses').as('myusers').out('plays').has('game', 'warcraft').select('myusers').by('name')

as('myusers') --> Provides a reference/alias to the vertices at this stage. Note that it does not store all the results at this stage instead it just provides a reference to the type of vertices at this point in the query.

out('plays').has('game', 'warcraft') --> Unlike previous time when we did not jump since we were using where, this time we jump onto the game vertices.

select('myusers').by('name') --> since we want to project the users but the current solutions are game vertices, we need to select the user vertices which we do using the reference we stored earlier.

Option 3: Start from user

g.V().hasLabel('user').where(out('plays').has('game','warcraft')).where(out('uses').has('console','ps3')).valueMap('name')

There are more ways to write this query such as using path() but I won't go into details here.

Since you are beginning to learn Gremlin, I would recommend that you start with https://kelvinlawrence.net/book/Gremlin-Graph-Guide.html