在 Neo4J 中切换关系

Question

I'm trying to implement follow/unfollow in Neo4J. I would like to write a query would toggle the relationship between two nodes.

I currently have the following query:

neoSession.writeTransaction(tx => tx.run('MATCH (me:User), (other:User) WHERE ID(me) = $me AND ID(other) = $other OPTIONAL MATCH (me)-[af:FOLLOWS]->(other) CALL apoc.do.when(af IS NULL, CREATE (me)-[f:FOLLOWS]->(other), DELETE af)', { me: req.user_id, other: req.body.user, datetime: Date.now() }));

Prettified query-only:

MATCH (me:User), (other:User) 
  WHERE ID(me) = $me AND ID(other) = $other 
OPTIONAL MATCH (me)-[af:FOLLOWS]->(other) 
CALL 
  apoc.do.when(
    af IS NULL, 
    CREATE (me)-[f:FOLLOWS]->(other), 
    DELETE af
  )

But this results in the error

Neo4jError: Invalid input '>' (line 1, column 169 (offset: 168))

"MATCH (me:User), (other:User) WHERE ID(me) = $me AND ID(other) = $other OPTIONAL MATCH (me)-[af:FOLLOWS]->(other) CALL apoc.do.when(af IS NULL, CREATE (me)-[f:FOLLOWS]->(other), DELETE af)"

Answer 1

The queries (last two arguments) to apoc.do.when() have to be strings, so quote each of them.

Also, in order for each of those queries to use those variables, you need to pass those variables in a parameter map as a 4th argument.

Each of the conditional queries must RETURN something, otherwise there will be no rows yielded and anything after would be a no-op.

The call must YIELD value , so that needs to be present, and last, a query cannot end with a procedure call, so you need to RETURN something.

This one should work, you can adjust it as needed:

MATCH (me:User), (other:User) 
  WHERE ID(me) = $me AND ID(other) = $other 
OPTIONAL MATCH (me)-[af:FOLLOWS]->(other) 
CALL 
  apoc.do.when(
    af IS NULL, 
    "CREATE (me)-[f:FOLLOWS]->(other) RETURN f", 
    "DELETE af RETURN null as f",
    {me:me, af:af}
  ) YIELD value
RETURN value.f as f