Cypher: Adding properties to relationship as distinct values - neo4j

Question

What I'm trying to do is to write a query - I already made it a webservice(working on local machine, so I get the name and people as parameters) - which connects people who share the same hobbies and set the hobbies as the relationship property as an array.
My first attempt was;
MERGE (aa:Person{name:$name})
WITH aa, $people as people
FOREACH (person IN people |
MERGE (bb:Person{name:person.name})
MERGE (bb)-[r:SHARESSAMEHOBBY]->(aa)
ON MATCH SET r.hobbies = r.hobbies + person.hobby
ON CREATE SET r.hobbies = [person.hobby])
However this caused duplicated property elements like ["swimming","swimming"]
I'm trying to set only unique properties. Then I tried the following query;
MERGE (aa:Person{name:$name})
WITH aa, $people as people FOREACH (person IN people | MERGE (bb:Person{name:person.name}) MERGE (bb)-[r:SHARESSAMEHOBBY]->(aa)
WITH r, COALESCE(r.hobbies, []) + person.hobby AS hobbies
UNWIND hobbies as unwindedHobbies
WITH r, collect(distinct, unwindedHobbies) AS unique
set r.as = unique)
However now it gives me syntax error;
errorMessage = "[Neo.ClientError.Statement.SyntaxError] Invalid use of WITH inside FOREACH
Any help is appreciated.

Answer 1

This should work:
MERGE (aa:Person {name: $name})
WITH aa
UNWIND $people AS person
MERGE (bb:Person {name: person.name})
MERGE (bb)-[r:SHARESSAMEHOBBY]-(aa)
WITH r, person, CASE
WHEN NOT EXISTS(r.hobbies) THEN {new: true}
WHEN NOT (person.hobby IN r.hobbies) THEN {add: true}
END AS todo
FOREACH(ignored IN todo.new | SET r.hobbies = [person.hobby])
FOREACH(ignored IN todo.add | SET r.hobbies = r.hobbies + person.hobby);
You actually had 2 issues, and the above query addresses both:
If a SHARESSAMEHOBBY relationship already existed in the opposite direction (from aa to bb), the following MERGE clause would have caused the unnecessary creation of a second SHARESSAMEHOBBY relationship (from bb to aa):
MERGE (bb)-[r:SHARESSAMEHOBBY]->(aa)
To avoid this, you should have used a non-directional relationship pattern (which is is permitted by MERGE, but not CREATE) to match a relationship in either direction, like this:
MERGE (bb)-[r:SHARESSAMEHOBBY]-(aa)
You needed to determine whether it is necessary to initialize a new hobbies list or to add the person.hobby value to an existing r.hobbies list that did not already have that value. The above query uses a CASE clause to assign to todo either NULL, or a map with a key indicating what additional work to do. It then uses a FOREACH clause to execute each thing to do, as appropriate.