Combine the result of match and use for further processing

Neo4j Graph Platform Cypher
1

I'm developing an SNS with neo4j, and would like to know how to achieve the case described below.
Please note that the use-case may not sound practical. It's because I'm trying to simplify the case. The actual conditions are much complicated, so I didn't want to write everything here.

Let's say I want to fetch all comments and its author by two conditions.

  1. I want a comment by andy
  2. I want a comment by my friends

To MATCH with multiple conditions, I have the following:

match (u1:User{name:'andy'})-[:CREATED]->(c1:Comment)
match (:User{name:'me'})-[:FRIENDS_WITH]->(u2:User)-[:CREATED]->(c2:Comment)
return u1,u2,c1,c2

However, to further process the User and Comment nodes, I want to pass these nodes with WITH, whilst combining them. Something like this would be ideal:

match (u1:User{name:'andy'})-[:CREATED]->(c1:Comment)
match (:User{name:'me'})-[:FRIENDS_WITH]->(u2:User)-[:CREATED]->(c2:Comment)
WITH (u1,u2) as u, (c1,c2) as c
...

Since that's not possible, I made several different attempts:

match (u1:User{name:'andy'})-[:CREATED]->(c1:Comment)
match (:User{name:'me'})-[:FRIENDS_WITH]->(u2:User)-[:CREATED]->(c2:Comment)
WITH collect(u1) + collect(u2) as u, collect(c1) + collect(c2) as c
UNWIND u
UNWIND c
...

But this would destroy the relation who created the comment, so doesn't work.

match p1=(u1:User{name:'andy'})-[:CREATED]->(c1:Comment)
match p2=(:User{name:'me'})-[:FRIENDS_WITH]->(u2:User)-[:CREATED]->(c2:Comment)
WITH p1+p2 as p
...

This doesn't work because + requires a list as argument.

UNION does not work because it must be followed by RETURN, but there's a ton of post-processing to do after this query.

How can I achieve such query?

2

You could try collecting on a map that contains the user and the relationship/comment perhaps. So something like this:

match (u1:User{name:'andy'})-[created:CREATED]->(c1:Comment)
match (:User{name:'me'})-[:FRIENDS_WITH]->(u2:User)-[created2:CREATED]->(c2:Comment)
WITH collect(u1) + collect(u2) as u, collect(c1) + collect(c2) as c

WITH collect({user: u1, relType: created, comment: c1}) +
          collect({user: u2, relType: created2, comment: c2})

Not sure if that's what you want?

2 Likes
3

Hello, here's an article on different ways to do post-UNION processing, that should have some workarounds you can use.

And just to note there are some features coming in 4.0 that will make this much easier to tackle.

4

Thank you mark!

I'm not sure how that query works. In the second WITH you are using u1, but the first WITH only passes u and c, so it doesn't work on my local environment...! :frowning:

Also wouldn't two consecutive MATCH mean BOTH conditions must be met?
I apologize my description wasn't detailed enough, but I need EITHER conditions met! :slight_smile: