How to implement propagation algorithms in Neptune

Question

I need to implement a custom propagation algorithm that starts from a given node and visits its neighbors and update their properties accordingly based on the previous node properties.
Example use case is, a quality flag that changed in a given node from good to bad and I need to make all the subsequent nodes become bad.

What is the recommend way of implement this efficiently in Neptune? (I'm trying to avoid to have client code to have this graph traversal one hop at a time)

Answer

So something like the following?

Sample graph:
```
g.addV('Product').property(id,'prod1').property('name','widget').property('quality','good').as('p1').
addV('Product').property(id,'prod2').property('name','sproket').property('quality','good').as('p2').
addV('Product').property(id,'prod3').property('name','screw').property('quality','good').as('p3').
addV('Product').property(id,'prod4').property('name','bolt').property('quality','good').as('p4').
addE('connectedTo').from('p1').to('p2').
addE('connectedTo').from('p1').to('p3').
addE('connectedTo').from('p1').to('p4')
```

Sample query:
```
g.V('prod1').as('p1').property(single,'quality','bad').
    out('connectedTo').
    property(single,'quality',select('p1').values('quality'))
```

This query would alter the property on the "root" vertex and apply the same property value to the children vertices.

UPDATE:  If wanting to propagate this down an entire tree, you could use a `repeat()` step:

```
g.V('prod1').as('p1').property(single,'quality','bad').
    repeat(
        out('connectedTo').
        property(single,'quality',select('p1').values('quality'))
    )
```

How to implement propagation algorithms in Neptune

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