在Neo4j 2.0中将可选节点与Cypher查询链接

Question

I'm trying to figure out the correct way to attach newly created nodes to additional nodes that may or may not exist. Basically, CREATE A and if B exists, LINK B to A and RETURN A. If B doesn't exist just RETURN A.

This is my Cypher query (the extra WITH clauses are because this is part of a larger query and I'm trying to make sure this sample code works the same way):

CREATE (a:A { foo: "bar" })
WITH a

OPTIONAL MATCH (b:B)
WHERE a.foo = b.foo
CREATE UNIQUE b-[:LINK]->a
WITH a

RETURN a

This doesn't work since the CREATE UNIQUE fails since b is NULL. Other than breaking it up into multiple queries, is there a way to accomplish this?

Answer 1

I think you need to hack it with foreach...

CREATE (a:A { foo: "bar" })
WITH a

OPTIONAL MATCH (b:B)
WHERE a.foo = b.foo
WITH a, collect(b) as bs
FOREACH(b in bs | CREATE UNIQUE b-[:LINK]->a)
WITH a

RETURN a