Neo4j 2.0 Cypher Query - CREATE within a FOREACH

[Rory Madden]

I'm having trouble with a cypher query. I want to replace one or more relationships, if they exists, with a new node and two new relationships. The query below tests if the relationship exists but it fails on the new node creation. The CREATE syntax works on its own but not nested within the FOREACH loop.

START s = node(1)

MATCH (u)-[r?:RELATED]->(s)

FOREACH (u in (CASE WHEN r<>NULL THEN [u] ELSE [] END):

CREATE (u)<-[:REL1]-(n {test:"test"})-[:REL2]->(s))

DELETE r

RETURN s

I get an error saying: Unknown identifier n

Does anyone know how to fix this?

[Andres Taylor]

Hi Rory,

I would do it like this:

START s = node(1) 

MATCH (u)-[r?:RELATED]-(s) 

DELETE r 

WITH collect(u) AS collectionOfU, s 

FOREACH (u IN collectionOfU : 

  CREATE (u)<-[:REL1]-({ test:"test" })-[:REL2]->(s)) 

RETURN s

The aggregate function COLLECT does what you are looking for - it creates a collection of the incoming values, ignoring any nulls.

Don't know why you are getting that weird error message - but we did have a bug around this some time ago. Have you tried on the latest stable version?

Andrés

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The best way to ask for Cypher help: http://console.neo4j.org/usage.html 

[Michael Hunger]

Also if you don't need the return results at all you can get by by using something much simpler:

START s = node(1)

MATCH (u)-[r:RELATED]->(s)

DELETE r

CREATE (u)<-[:REL1]-(n {test:"test"})-[:REL2]->(s))

[Rory Madden]

Thanks for your responses. This helped me to sort out the problem.