CODEWITHSUNDEEP
neo4jcypher
pewpewlasers
pewpewlasers

Reputation: 3215

Neo4j values from WITH disappears if subsequent MATCH fails

I ran into this issue I have a cypher that passes on data using WITH

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
RETURN connected

This works. When KNOWS relationship is created, connected is true else false. And so either true or false is returned by this cypher. Now I want to extend this 

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
WITH y, connected
MATCH (x)-[zz:LIKES]->(y)    <------------- this match
WITH zz, connected
RETURN zz, connected

NOW connected returns true or false only if the marked match succeeds. Otherwise it gives an empty result. I want connected to return true or false regardless of whether MATCH succeeds or not.

EDIT:

Sorry I left out something in the second query.

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
WITH y, connected
MATCH (x)-[zz:LIKES]->(y)    <------------- this match
MERGE x-[:LOVES]->(y)        <------------- EDIT
WITH zz, connected
RETURN zz, connected

Optional match while solves the match issue, it will fail with merge giving null error. Any suggestions?

Upvotes: 1

Views: 150

Answers (1)

Mark Needham
Mark Needham

Reputation: 2128

I think something like this may do the trick. 

MATCH (u1:user {username: "pewpewlasers"}), (u2:user {username: "pewpew2"})
MERGE (u1)-[y:KNOWS]->(u2)
ON CREATE SET y.connected = 1
WITH y, has(y.connected) AS connected 
REMOVE y.connected
WITH y, connected
OPTIONAL MATCH (x)-[zz:LIKES]->(yy)
FOREACH(ignoreMe IN CASE WHEN yy IS null THEN [] ELSE [1] END |
    MERGE x-[:LOVES]->(yy))
WITH zz, connected
RETURN zz, connected

OPTIONAL MATCH allows you to keep all your initial rows and then you'll have a null value for 'zz' if there is no relationship.

Upvotes: 3

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