CODEWITHSUNDEEP
neo4jcypher
Aerodynamika
Aerodynamika

Reputation: 8423

How to update a relation property in Neo4J Cypher?

I have the following Neo4J Cypher query:

MATCH (u:User {uid: $userId}) 
UNWIND $contextNames as contextName 
MERGE (context:Context {name:contextName.name,by:u.uid,uid:contextName.uid}) 
ON CREATE SET context.timestamp=$timestamp 
MERGE (context)-[:BY{timestamp:$timestamp}]->(u)

The last string always creates a new relation between the context and the u node. However, what if I just want to update it? How do I integrate this logic into the query above?

Do I have to add WITH context,u before the MERGE and then add rel:BY into the query?

Or do MATCH (context)-[rel:BY.... and then update the rel?

Just looking for the most efficient "best practices" way to do that.

Thanks!

Upvotes: 0

Views: 178

Answers (1)

Stephan
Stephan

Reputation: 311

There are two possible situation which might occur:

  1. A relation between context and u is already present
  2. A relation between context and u is not yet present (this will happen when contextwas just created by merge)

When you run the following line

MERGE (context)-[:BY{timestamp:$timestamp}]->(u)

Neo4j will check if there is already a relation BY in place between context and u with the given timestamp value. If yes, no new relation will be created. I guess that the timestamp is not a proper identifier for matching a relation, especially since you write that you want to update it. Therefore, I recommend to update the query in the following way:

MATCH (u:User {uid: $userId}) 
UNWIND $contextNames as contextName 
MERGE (context:Context {name:contextName.name,by:u.uid,uid:contextName.uid}) 
ON CREATE SET context.timestamp=$timestamp 
MERGE (context)-[by:BY]->(u)
SET by.timestamp=$timestamp

This way, a relation will be created if not already present. Either way, the timestamp will be set to the specified value.

Upvotes: 1

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