How can I write a conditional UPDATE STATEMENT in Gremlin

Question

How can I write a gremlin query to update the status value to "shared" whenever the product is shared by the user. When the product isn't shared, I want the status to have a different value. Will I need to set a default and update value in the same query?

I have shared my vertex label and edge label, and a diagram of my vertex.

NeptuneUserVertexLabel = "user"
NeptuneProductVertexLabel = "product"
NeptuneProductSharedByEdgeLabel = "productsharedby"

Do you want to set this property at the time the edge is added? In terms of data modeling the presence of the edge indicates that the product has been shared. What is the purpose of also adding a property? It seems a bit redundant. — Kelvin Lawrence, Sep 13 '21 at 12:13

Kelvin Lawrence · Accepted Answer · 2021-09-13T21:07:39.933

Here is an example of one way you might do it, but as I mentioned in my comment above, the presence of one or more edges really indicates the same thing that a shared property might indicate.

Assuming this small graph

g.addV('Product').property('shared',false).property('pid','p1').as('p1').
  addV('User').property('name','Name').property('uid','u1').as('u1').
  addE('SharedBy').from('p1').to('u1')

You can do

gremlin> g.V().has('pid','p1').coalesce(filter(out('SharedBy')).property('shared',true),property('shared',false))
==>v[61293]

gremlin> g.V().has('pid','p1').valueMap()
==>[shared:[true],pid:[p1]]

We can drop the edge and re run the query to prove it works

gremlin> g.E(61299).drop()

gremlin> g.V().has('pid','p1').coalesce(filter(out('SharedBy')).property('shared',true),property('shared',false))
==>v[61293]

gremlin> g.V().has('pid','p1').valueMap()
==>[shared:[false],pid:[p1]]

Note that it is not required that the property already exist in some form. I included it that way in my example but that is totally optional. It is usually faster to check for the existence rather than the non-existence of a property however so that is something to consider. A tradeoff between efficiency and storing potentially a lot of extra properties in the graph.

How can I write a conditional UPDATE STATEMENT in Gremlin

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