How to Assign Traversal Results to Variables in Gremlin?

  

When working with Apache TinkerPop and its graph traversal language Gremlin, one of the most common beginner mistakes is forgetting to terminate the traversal before assigning it to a variable. Let's use following domain model to demo this.

 

1. E-Commerce Domain Model Overview

To demonstrate the example, we will use a simple e-commerce domain model built using an in-memory TinkerGraph. This model is intentionally small but expressive enough to showcase real-world traversal patterns.

 

At a high level, the graph represents:

 

·      Customers placing orders

·      Orders containing products

·      Products belonging to categories

·      Orders being delivered to cities

 

This gives us multiple vertex labels, relationships, and property types to work with and ideal for exploring how valueMap() behaves across different scenarios.

 

Vertex Types

·      City: Represents delivery locations

·      Category: Represents product categories

·      Product: Represents items that can be purchased

·      Customer: Represents users of the platform

·      Order: Represents purchase transactions

 

Each vertex label has a small and focused set of properties, which makes it easier to see how valueMap() returns property data and how WithOptions affects the output.

 

Edge Types and Relationships

·      belongsTo: Connects a product to its category

·      placed: Connects a customer to an order

·      contains: Connects an order to one or more product vertices. An order may contain multiple products

·      deliveredTo: Connects an order to a city, represents the delivery destination for the order

 

Gremlin Code to build the Graph

graph = TinkerGraph.open()
g = graph.traversal()

blr = g.addV('city').property('name', 'Bengaluru').next()
hyd = g.addV('city').property('name', 'Hyderabad').next()
chn = g.addV('city').property('name', 'Chennai').next()
pne = g.addV('city').property('name', 'Pune').next()

catElectronics = g.addV('category').property('name', 'Electronics').next()
catBooks       = g.addV('category').property('name', 'Books').next()
catClothing    = g.addV('category').property('name', 'Clothing').next()

p1 = g.addV('product').property('sku', 'P1001').property('name', 'Laptop').next()
p2 = g.addV('product').property('sku', 'P1002').property('name', 'Smartphone').next()
p3 = g.addV('product').property('sku', 'P2001').property('name', 'Java Programming Book').next()
p4 = g.addV('product').property('sku', 'P3001').property('name', 'T-Shirt').next()

g.V(p1).addE('belongsTo').to(catElectronics).next()
g.V(p2).addE('belongsTo').to(catElectronics).next()
g.V(p3).addE('belongsTo').to(catBooks).next()
g.V(p4).addE('belongsTo').to(catClothing).next()


c1 = g.addV('customer').property('customerId', 'C101').property('name', 'Amit Sharma').next()
c2 = g.addV('customer').property('customerId', 'C102').property('name', 'Priya Iyer').next()
c3 = g.addV('customer').property('customerId', 'C103').property('name', 'Rohit Verma').next()

o1 = g.addV('order').property('orderId', 'O9001').next()
o2 = g.addV('order').property('orderId', 'O9002').next()
o3 = g.addV('order').property('orderId', 'O9003').next()
o4 = g.addV('order').property('orderId', 'O9004').next()
o5 = g.addV('order').property('orderId', 'O9005').next()

g.V(c1).addE('placed').to(o1).next()
g.V(c1).addE('placed').to(o2).next()

g.V(c2).addE('placed').to(o3).next()

g.V(c3).addE('placed').to(o4).next()
g.V(c3).addE('placed').to(o5).next()


g.V(o1).addE('contains').to(p1).next()
g.V(o1).addE('contains').to(p3).next()

g.V(o2).addE('contains').to(p2).next()

g.V(o3).addE('contains').to(p4).next()

g.V(o4).addE('contains').to(p1).next()
g.V(o4).addE('contains').to(p4).next()

g.V(o5).addE('contains').to(p3).next()


g.V(o1).addE('deliveredTo').to(blr).next()
g.V(o2).addE('deliveredTo').to(blr).next()

g.V(o3).addE('deliveredTo').to(hyd).next()

g.V(o4).addE('deliveredTo').to(chn).next()

g.V(o5).addE('deliveredTo').to(pne).next()

gremlin> g.V().valueMap(true)
==>[id:0,label:city,name:[Bengaluru]]
==>[id:33,label:customer,customerId:[C102],name:[Priya Iyer]]
==>[id:2,label:city,name:[Hyderabad]]
==>[id:4,label:city,name:[Chennai]]
==>[id:36,label:customer,customerId:[C103],name:[Rohit Verma]]
==>[id:6,label:city,name:[Pune]]
==>[id:39,label:order,orderId:[O9001]]
==>[id:8,label:category,name:[Electronics]]
==>[id:41,label:order,orderId:[O9002]]
==>[id:10,label:category,name:[Books]]
==>[id:43,label:order,orderId:[O9003]]
==>[id:12,label:category,name:[Clothing]]
==>[id:45,label:order,orderId:[O9004]]
==>[id:14,label:product,name:[Laptop],sku:[P1001]]
==>[id:47,label:order,orderId:[O9005]]
==>[id:17,label:product,name:[Smartphone],sku:[P1002]]
==>[id:20,label:product,name:[Java Programming Book],sku:[P2001]]
==>[id:23,label:product,name:[T-Shirt],sku:[P3001]]
==>[id:30,label:customer,customerId:[C101],name:[Amit Sharma]]
gremlin> 
gremlin> 
gremlin> g.E().valueMap(true)
==>[id:64,label:deliveredTo]
==>[id:65,label:deliveredTo]
==>[id:49,label:placed]
==>[id:50,label:placed]
==>[id:51,label:placed]
==>[id:52,label:placed]
==>[id:53,label:placed]
==>[id:54,label:contains]
==>[id:55,label:contains]
==>[id:56,label:contains]
==>[id:57,label:contains]
==>[id:26,label:belongsTo]
==>[id:58,label:contains]
==>[id:27,label:belongsTo]
==>[id:59,label:contains]
==>[id:28,label:belongsTo]
==>[id:60,label:contains]
==>[id:29,label:belongsTo]
==>[id:61,label:deliveredTo]
==>[id:62,label:deliveredTo]
==>[id:63,label:deliveredTo]

Use Case 1: Get All Orders Delivered to Bengaluru

orders = g.V().
  hasLabel('city').
  has('name', 'Bengaluru').
  in('deliveredTo')

Above snippet stores the traversal in orders variable, not the result

gremlin> orders = g.V().
......1>   hasLabel('city').
......2>   has('name', 'Bengaluru').
......3>   in('deliveredTo')
==>v[39]
==>v[41]
gremlin> 
gremlin> orders
gremlin> 
gremlin> orders.getClass()
==>class org.apache.tinkerpop.gremlin.groovy.loaders.SugarLoader$GraphTraversalCategory

To store the correct result we need to terminate the traversal.

orders = g.V().
  hasLabel('city').
  has('name', 'Bengaluru').
  in('deliveredTo').
  toList()

gremlin> orders = g.V().
......1>   hasLabel('city').
......2>   has('name', 'Bengaluru').
......3>   in('deliveredTo').
......4>   toList()
==>v[39]
==>v[41]
gremlin> 
gremlin> orders
==>v[39]
==>v[41]
gremlin> 
gremlin> orders.getClass()
==>class java.util.ArrayList

   

We can print each order details with the traversal.

 

orders.each {
    println g.V(it).valueMap(true).next()
}

gremlin> orders.each {
......1>     println g.V(it).valueMap(true).next()
......2> }
[id:39, label:order, orderId:[O9001]]
[id:41, label:order, orderId:[O9002]]

   

Use Case 2: Print Products Ordered by Amit Sharma

 

Let's get 'Amit Sharma' vertex.

 

amit = g.V().
         hasLabel('customer').
         has('name', 'Amit Sharma').
         next()

   

Get the orders by Amit Sharma.

 

amitOrders = g.V(amit).
  out('placed').
  toList()

   

Print the orders details.

 

amitOrders.each {
    println g.V(it).valueMap(true).next()
}

gremlin> amit = g.V().
......1>          hasLabel('customer').
......2>          has('name', 'Amit Sharma').
......3>          next()
==>v[30]
gremlin> 
gremlin> amitOrders = g.V(amit).
......1>   out('placed').
......2>   toList()
==>v[39]
==>v[41]
gremlin> 
gremlin> 
gremlin> amitOrders.each {
......1>     println g.V(it).valueMap(true).next()
......2> }
[id:39, label:order, orderId:[O9001]]
[id:41, label:order, orderId:[O9002]]
==>v[39]
==>v[41]

   

Print Orders with Products Inside Them.

 

amitOrders.each { order -> {
    println "Order: " + order.value('orderId')
    
    g.V(order).
      out('contains').
      values('name').
      toList().
      each { println "  Product: " + it }
    }
}

gremlin> amitOrders.each { order -> {
......1>     println "Order: " + order.value('orderId')
......2>     
......2>     g.V(order).
......3>       out('contains').
......4>       values('name').
......5>       toList().
......6>       each { println "  Product: " + it }
......7>     }
......8> }
Order: O9001
  Product: Laptop
  Product: Java Programming Book
Order: O9002
  Product: Smartphone
==>v[39]
==>v[41]

   

Use Case 3: Get First 2 Products Only

next(2) return 2 elements in the traversal, next(n) will return the n elements in the traversal.

 

first2Products = g.V().
                   hasLabel('product').
                   next(2)


first2Products.each {product -> {
    println product.value('name')
}}

gremlin> first2Products = g.V().
......1>                    hasLabel('product').
......2>                    next(2)
==>v[14]
==>v[17]
gremlin>
gremlin> first2Products.each {product -> {
......1>     println product.value('name')
......2> }}
Laptop
Smartphone
==>v[14]
==>v[17]

   

In the Gremlin Console, you can view all currently defined variables by running the command ":show variables".

  

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