CODEWITHSUNDEEP
neo4jcypher
superkruger
superkruger

Reputation: 369

Neo4J two way relationship query with cypher

I have a two-way [:FRIENDSHIP] relationship between User nodes:

(UserA)<-[:FRIENDSHIP {approved:true}]->(UserB)

Here's a little test function in Java to setup the relationship:

public void approveFriendship(User requestor, User requestee) {
    Friendship friendship = new Friendship(requestor, requestee);
    friendship.setApproved(true);

    Friendship invertedFriendship = new Friendship(requestee, requestor);
    invertedFriendship.setApproved(true);

    requestor.getFriendships().add(friendship);
    requestee.getFriendships().add(invertedFriendship);

    userRepository.save(requestor);
    userRepository.save(requestee);
}

This cypher query returns the friends of UserA, and works fine:

start user=node({0})
match (user)-[r?:FRIENDSHIP]->(friends)
where r.approved = true
return friends

This cypher query returns the posts of a friend, and does not work (returns empty result):

start n=node({0})
match (n)<-[r?:FRIENDSHIP]->(friend)<-[:AUTHOR]-(friendposts)
where r.approved = true
return friendposts order by friendposts.createdAt

When omitting the where r.approved = true line or changing it to where r.approved = false it returns posts of friends without the approved status in both cases.

Can anybody spot if I'm doing something wrong here? Much obliged.

Upvotes: 0

Views: 1389

Answers (1)

superkruger
superkruger

Reputation: 369

Solved it.

Dunno why, but in a one-to-many type relationship (eg. User to Post) Neo4J prefers outgoing relationships on the Collection, and the incoming on the single entity. I had it the other way round...

Now my classes look like this:

public class User {
    @RelatedTo(type = "AUTHOR")
    private Set<Post> posts;
}

public class POST {
    @RelatedTo(type = "AUTHOR", direction = Direction.INCOMING)
    private User author;
}

And of course the cypher query has to change to reflect the new relationship direction (note arrow behind author):

start n=node({0})
match (n)<-[r?:FRIENDSHIP]->(friend)-[:AUTHOR]->(friendposts)
where r.approved = true
return friendposts order by friendposts.createdAt

Upvotes: 2

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