CODEWITHSUNDEEP
neo4jcyphergraph-databases
Silta
Silta

Reputation: 99

Neo4j create node if not exist on relationship creation

With Neo4J, when creating a relationship, I would like to create a node if it does not exist. I can do this using MERGE, but I would like the created node to be of a different type. Is there a way to check if the node exists and create a different node if not.

My current request:

MATCH (a:Person {name:'Jon'})
MERGE (b:City {name: 'Paris'})
CREATE (a)-[:work]->(b)

Here we assume that the person exists in all cases, but the city not necessarily. This request works and creates a new city if it does not exist.

My problem is that I want to keep a track of the new city by giving them the type "NewCity" instead of "City".

Upvotes: 0

Views: 1027

Answers (1)

fbiville
fbiville

Reputation: 8950

Ideally, you would write it like this:

MATCH (a:Person {name:'Jon'})
MERGE (b:City {name: 'Paris'})
ON CREATE
    SET b:NewCity
ON MATCH
    REMOVE b:NewCity // <-- spoiler alert: this does NOT work :(
CREATE (a)-[:work]->(b)

You need to keep the City label when you first create the node, otherwise the next time the query runs, MERGE won't match the node anymore.

Unfortunately, ON MATCH REMOVE b:NewCity is not supported, so you have to introduce an extra SET that gets removed afterwards:

MERGE (b:City {name: 'Paris'})
ON CREATE
    SET b:NewCity
ON MATCH
    SET b.temp = ''
WITH *
CALL { WITH b
  WITH b WHERE b.temp IS NOT NULL
  REMOVE b.temp
  REMOVE b:NewCity
}

Upvotes: 1

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