Case Statement For Null relationship

[MuddyBootsCode]

I'm trying to perform an operation that will check to see if a relationship exists on a node and if not create one. If a relationship does exist, I want to delete the relationship and then create a new one. What I have so far is:

Match (w:Well {id: "0099"})<-[r:OPERATES]-()
return r
CASE r
WHEN r is null THEN with w as free_well match (o:Operator {id: "cdf90d9e-6d07-11e9-b13d-00e04c680cd0"}) merge (free_well)<-[:OPERATES]-(o) return o
ELSE delete r with w as free_well match (o:Operator {id: "cdf90d9e-6d07-11e9-b13d-00e04c680cd0"})
merge (free_well)<-[:OPERATES]-(o)
return o
END

which does not work. I realize that that I may not be able to test against just the relationship but I'm not sure what else to check for. The following statement does what I want to do as long as a relationship exists but if one doens't the statement doesn't do anything.

Match (w:Well {id: $wellId})<-[r:OPERATES]-()
 delete r
 with w as free_well
 match (o:Operator {id: $operatorId})
 merge (free_well)<-[:OPERATES]-(o)
 return o

So I'm trying to make one that will do it regardless of the relationship state.

[andrew_bowman]

You'll need to mix MATCH and OPTIONAL MATCH here, using MATCH on the node itself and OPTIONAL MATCH on the pattern including the might-not-exist relationship:

Match (w:Well {id: $wellId})
OPTIONAL MATCH (w)<-[r:OPERATES]-()
 delete r
 with DISTINCT w as free_well
 match (o:Operator {id: $operatorId})
 merge (free_well)<-[:OPERATES]-(o)
 return o

Alternately you could use a FOREACH, and use a pattern comprehension as the list source of the :OPERATES relationships on w:

Match (w:Well {id: $wellId})
FOREACH (rel in [(w)<-[r:OPERATES]-() | r] | DELETE rel)
 with w as free_well
 match (o:Operator {id: $operatorId})
 merge (free_well)<-[:OPERATES]-(o)
 return o

[MuddyBootsCode]

Thanks will give it a shot and report back.

[MuddyBootsCode]

andrew.bowman:

Match (w:Well {id: $wellId}) OPTIONAL MATCH (w)<-[r:OPERATES]-() delete r with DISTINCT w as free_well match (o:Operator {id: $operatorId}) merge (free_well)<-[:OPERATES]-(o) return o

Worked like a charm, thank you.