neo4j - Neo4j: return error if no matching nodes found when creating a relationship?

Question

Apologies if this has already been asked, but I was unable to find the answer

I would like to error when trying to create a relationship between nodes, where one or both of the nodes do not exist

For example, the following code just returns no results, but I would like it to raise an error to let me know that these nodes do not exist, so that I can surface that error to my application:

MATCH (user1: User{uuid: '123'}), (user2: User{uuid: '456'})
CREATE (user1)-[:LIKES]->(user2)

Please assume that the database is empty and therefore no nodes were matched

I tried to add a constraint, but I didn't know how to approach it and if this is possible - are you able to help please?

Answer 1

当成功找到两个节点时，您的查询可以返回一些东西（如新关系），而不是错误。如果查询没有返回任何内容，则意味着一个或两个节点不存在。

例如：

MATCH (user1: User{uuid: '123'}), (user2: User{uuid: '456'})
CREATE (user1)-[r:LIKES]->(user2)
RETURN r;