I am trying to make a database where every time a node doesn't exist it will create a new one and set a relationship between this node and another. If the node exists, both nodes get a relationship.
My problem is that, if I try to connect 2 existing nodes, the 2nd node will be recreated. I tried with MERGE and CREATE UNIQUE, both didn't work.
My example code:
CREATE (test1 name:'1'})
MATCH (n)
WHERE n.name = '1'
MERGE (n)-[:know {r:'123'}]->(test3 {name:'3'})
MATCH (n)
WHERE n.name = '1'
MERGE (n)-[:know {r:'123'}]->(test2 {name:'2'})
Till here it works but with:
MATCH (n)
WHERE n.name = '3'
MERGE (n)-[:know {r:'123'}]->(test2 {name:'2'})
it creates a new node "2" instead of connecting to the existing one.
When using MERGE on full patterns, the behavior is that either the whole pattern matches, or the whole pattern is created. MERGE will not partially use existing patterns — it’s all or nothing. If partial matches are needed, this can be accomplished by splitting a pattern up into multiple MERGE clauses. http://docs.neo4j.org/chunked/stable/query-merge.html
MERGE (n)-[:know {r:'123'}]->(test2 {name:'2'}) will try to match the entire pattern and since it does not exist, it creates it. What you can do is:
MERGE (n {name: '3'}) //Create if a node with name='3' does not exist else match it
MERGE (test2 {name:'2'}) //Create if a node with name='2' does not exist else match it
MERGE (n)-[:know {r:'123'}]->(test2) //Create the relation between these nodes if it does not already exist