Neo4j: get all relations between queried nodes

Question

I want to make a cypher query that do below tasks:

there is a given start node, and I want to get all related nodes in 2 hops
sort queried nodes by hops asc, and limit it with given number
and get all relations between result of 1.

I tried tons of queries, and I made below query for step 1, 2

MATCH path=((start {eid:12018})-[r:REAL_CALL*1..2]-(end))
WITH start, end, path
ORDER BY length(path) ASC
RETURN start, collect(distinct end)[..10]

But when I try to get relationships in queried path with below query, it returns all relationships in the path :

MATCH path=((start {eid:12018})-[r:REAL_CALL*1..2]-(end))
WITH start, end, path
ORDER BY length(path) ASC
RETURN start, collect(distinct end)[..10], relationships(path)

I think I have to match again with result of first match instead of get relationships from path directly, but all of my attempts have failed.

How can I get all relationships between queried nodes? Any helps appreciate, thanks a lot.

cybersam · Accepted Answer · 2017-09-08 19:15:34Z

1

[EDITED]

Something like this may work for you:

MATCH (start {eid:12018})-[rels:REAL_CALL*..2]-(end)
RETURN start, end, COLLECT(rels) AS rels_collection
ORDER BY
  REDUCE(s = 2, rs in rels_collection | CASE WHEN SIZE(rs) < s THEN SIZE(rs) ELSE s END)
LIMIT 10;

The COLLECT aggregation function will generate a collection (of relationship collections) for each distinct start/end pair. The LIMIT clause limits the returned results to the first 10 start/end pairs, based on the ORDER BY clause. The ORDER BY clause uses REDCUE to calculate the minimum size of each path to a given end node.

edited Sep 8, 2017 at 19:15

answered Sep 7, 2017 at 19:53

cybersam

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10 Comments

Rosicky Over a year ago

Thank you for your answer. Your query works fine, but limit has some problem. 'end' nodes are limited by 10 correctly with my query, but when I tested your query, it only displays 8 nodes. I think limit clause counts not only nodes but also relationships. Do you know how can I apply limit clause only for number of nodes?

cybersam Over a year ago

If I understand what you want, my updated answer should work.

Rosicky Over a year ago

Thank you for your kind explanation. Now I understand limit / order by clauses much better than before with your explanation. I'll try it. Thanks a lot!

Rosicky Over a year ago

As a result of your query, it limits end nodes correctly, but there is ordering problem. Actually I want to get nodes within 1 hop first in limit value, after then get 2 hop nodes. For example, if there are 10 nodes - 6 nodes in distance 1, 4 nodes in distance 2, and limit number is 8, then I want to aggregate 6 nodes in distance 1 first, and after then aggregate 2 nodes in distance 2. So I used length(path) ASC because of this requirement. Could you give me an advice to handle it?

cybersam Over a year ago

OK, nice problem. I have updated my answer yet again, The COLLECT function seems to mess up the ordering, so the new query no longer orders before doing the COLLECT, but afterwards.

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