CODEWITHSUNDEEP
gremlintinkerpop3gremlin-java
Thirumal
Thirumal

Reputation: 9676

How to add new vertex using gremlin coalesce when the traversal is empty?

I am using @GremlinDsl so my traversal from g.V().hasLabel('NEW'), so I am using coalesce to add new vertices. It works well when there is any vertex with the given LABEL in the database, otherwise, it throws an exception. It's obvious the traversal is empty from g.V().hasLabel('NEW').

g.V().hasLabel('NEW').coalesce(__.V().hasId('T12321321R'),
__.addV('NEW')
.property(T.id, 'T12321321R'))

How to solve this, when we create the given vertex(Label) for the first time in the database? Any idea?

Upvotes: 0

Views: 94

Answers (1)

PrashantUpadhyay
PrashantUpadhyay

Reputation: 877

You need conditional write through fold and unfold.

gremlin> g.V()

gremlin> g.V().
......1>   hasLabel('NEW').
......2>   hasId('T12321321R').
......3>   fold().
......4>   coalesce(unfold(), addV('NEW').property(T.id, 'T12321321R'))
==>v[T12321321R]

gremlin> g.V()
==>v[T12321321R]

gremlin> g.V().
......1>   hasLabel('NEW').
......2>   hasId('T12321321R').
......3>   fold().
......4>   coalesce(unfold(), addV('NEW').property(T.id, 'T12321321R'))
==>v[T12321321R]

gremlin> g.V()
==>v[T12321321R]

Upvotes: 2

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