Is it possible to determine if a Cypher MERGE results in a create or a match?

cypher, neo4j

Solution

I think that's contrary to the intention of `MERGE`. You would use it to describe what you want the graph to look like after your query has executed, not to find out what it looks like before–read and write operations are supposed to be kept strictly apart in Cypher. That said, you can set a dummy property like @LameCoder mentioned:

MERGE (u:User {id_str:"123"}) 
  ON CREATE SET u.onCreate = true
WITH u, exists(u.onCreate) as onCreate
REMOVE u.onCreate
RETURN u, onCreate

will return `(u), true` if created, `(u), false` if not, and leave no side effects. Or you can maintain timestamps, perhaps one for node creation and one for when the node was last modified–I think that's an example from the documentation. This

MERGE (u:User {id_str:"123"}) 
  ON CREATE SET u.created = timestamp()
  ON MATCH SET u.lastModified = timestamp()
RETURN u, has(u.lastModified) as onMerge

would be similar to the query above.

Problem

Consider the Neo4J 2.0 Cypher query ``` MERGE (u:User {id_str:"123"}) ON CREATE SET u.name="Bob", ON MATCH SET u.phone_num="555-4152" RETURN u ``` It's a silly query - don't worry about the intent here. The question is, how do I understand whether this query created or simply found a node? UPDATE Perhaps I should further motivate why I want this behavior. Here's why: If the node already exists, then don't have to go to a remote server (Twitter API in my case) and download all of the user's metadata. It would be nice if the ON CREATE could somehow link back out to a callback to pull down this data. It seems unlikely that this behavior is achievable in Cypher. So probably what I'll want to do is do a match, and if the get comes back NULL, then I'll call out to the Twitter API, get the metadata and do a create.

Original source