Neo4j - traversal to find friends of friends that are not friends with the user yet - neo4j

Question

Using Neo4j 2.0.1, I'm trying to find friends of friends that are not friends with the user yet at depth of any level(2-5).
At first, I used cypher to get all friends of friends but sadly the performance was so bad when I tried to find friends of friends at depth of 4 and 5. So, I moved from cypher to traversal rest api and later I will use in Neo4jPHP traversal. So this is the change I made:
Note:
- there are 10 users with 5 friends of each user
- user that I want to traverse at depth of 3 is 1
- traversal at depth of 3
Friends List:
User | Friends
1 | 9,2,8,7,5
2 | 1,6,3,8,10
3 | 5,7,1,10,2
4 | 3,10,6,9,5
5 | 4,8,1,9,3
6 | 7,9,3,2,10
7 | 9,5,10,6,8
8 | 6,9,1,10,5
9 | 6,5,10,1,8
10 | 8,6,4,5,9
Cypher:
MATCH (U:User)-[F:Friend]->(FU:User)-[FF:Friend]->(FFU:User)
WHERE U.user_id=1
WITH DISTINCT U, FFU
WHERE FFU<>U
WITH DISTINCT U, FFU
MATCH (FFU:User)-[FFF:Friend]->(FFFU:User)
WHERE FFFU<>U AND NOT (U)-[:Friend]->(FFFU)
RETURN DISTINCT FFFU.username;
Travesal Rest Api[UPDATED]:
POST http://localhost:7474/db/data/node/1/traverse/node
{
"order" : "breadth_first",
"uniqueness" : "node_global",
"prune_evaluator" : {
"name" : "none",
"language" : "builtin"
},
"return_filter" : {
"body" : "position.endNode().getProperty('user_id')!=1 && position.endNode().getProperty('user_id')!=9 && position.endNode().getProperty('user_id')!=2 && position.endNode().getProperty('user_id')!=8 && position.endNode().getProperty('user_id')!=7 && position.endNode().getProperty('user_id')!=5;",
"language" : "javascript"
},
"relationships" : {
"direction" : "out",
"type" : "Friend"
},
"max_depth" : 3
}
Neo4jPHP Traversal[UPDATED]:
$traversal->addRelationship('Friend', Relationship::DirectionOut)
->setPruneEvaluator(Traversal::PruneNone)
->setReturnFilter('javascript', "position.endNode().getProperty('user_id')!=1 && position.endNode().getProperty('user_id')!=9 && position.endNode().getProperty('user_id')!=2 && position.endNode().getProperty('user_id')!=8 && position.endNode().getProperty('user_id')!=7 && position.endNode().getProperty('user_id')!=5;")
->setMaxDepth(3)
->setUniqueness(Traversal::UniquenessNodeGlobal)
->setOrder(Traversal::OrderBreadthFirst);
Using the Traversal Rest Api and Neo4jPHP Traversal above I got the result: 9,6,7,3,2,10,5,4,8
While the result I want is: 6,3,10,4
Because 9,7,2,5,8 are already friends with the user: 1
NOTE:
I just updated the way I traverse my graph to find friends of friends at depth of 3, so I updated my question too.
We can see that conditions I made in return_filter is manually:
"body" : "position.endNode().getProperty('user_id')!=1 && position.endNode().getProperty('user_id')!=9 && position.endNode().getProperty('user_id')!=2 && position.endNode().getProperty('user_id')!=8 && position.endNode().getProperty('user_id')!=7 && position.endNode().getProperty('user_id')!=5;"
While in Cypher, we can easily remove friends of friends that are already friends with user: 1:
WHERE NOT (U)-[:Friend]->(FFFU)
Now, how to make a condition like that in Traversal Rest Api?
I ask because not much info from the documentation.
Please anyone help me. I really need your help.
Thank you.

Answer 1

Shouldn't this be possible by simply specifying:
MATCH (user:User)-[:FRIEND*2..4]->(fof)
WHERE NOT (user)-[:FRIEND]->(fof)
Or perhaps I'm missing something, are you using the DISTINCT statements as a way to improve performance? I'm surprised cypher is not performing well for you here, would you be able to try your query with the PROFILE command in the Neo4j shell, and send me the result? You can email me at jakewins AT gmail.com
As for the traversal, conceptually, I would do this:
Start at User
Find all Users friends, and put them in a Set 'friends'
Start at each friend, and traverse out as many hops you like
Return each user found that is not in the set of friends
I don't believe you can do the set part in the REST traversal API, which means you either need to write a server extension, which will allow you to write this in Java and use the more powerful Java traversal API, you can read about extensions here: http://docs.neo4j.org/chunked/stable/server-unmanaged-extensions.html and the Java traversal API here: http://docs.neo4j.org/chunked/stable/tutorial-traversal-java-api.html
Alternatively, you can do two calls, one to fetch all the users friends, and one to do the REST traversal with the users friends as part of the script you send over, like you do in your question but with your app generating the filter code.