CODEWITHSUNDEEP
neo4jcypher
Valentin Grégoire
Valentin Grégoire

Reputation: 1150

Neo4j - Get certain nodes and relations

I have an application where nodes and relations are shown. After a result is shown, nodes and relations can be added through the gui. When the user is done, I would like to get all the data from the database again (because I don't have all data by this point in the front-end) based on the Neo4j id's of all nodes and links. The difficult part for me is that there are "floating" nodes that don't have a relation in the result of the gui (they will have relations in the database, but I don't want these). Worth mentioning is that on my relations, I have the start and end node id. I was thinking to start from there, but then I don't have these floating nodes. Let's take a look at this poorly drawn example image: Poorly drawn example

As you can see:

Let's assume that:

Keeping in mind that behind the real data, there are way more relations between all these nodes, how can I recreate this very image again via Neo4j? I have tried doing something like: 

match path=(n)-[rels*]-(m)
where id(n) in [1, 2, 3, 4, 5]
and all(rel in rels where id in [11, 12, 13, 14])
and id(m) in [1, 2, 3, 4, 5]
return path

However, this doesn't work properly because of multiple reasons. Also, just matching on all the nodes doesn't get me the relations. Do I need to union multiple queries? Can this be done in 1 query? Do I need to write my own plugin?

I'm using Neo4j 3.3.5.

Upvotes: 0

Views: 1009

Answers (1)

cybersam
cybersam

Reputation: 66947

You don't need to keep a list of node IDs. Every relationship points to its 2 end nodes. Since you always want both end nodes, you get them for free using just the relationship ID list.

This query will return every single-relationship path from a relationship ID list. If you are using the neo4j Browser, its visualization should knit together these short paths and display your original full paths.

MATCH p=()-[r]-()
WHERE ID(r) IN [11, 12, 13, 14]
RETURN p

By the way, all neo4j relationships have a direction. You may choose not to specify the direction when you create one (using MERGE) and/or query for one, but it still has a direction. And the neo4j Browser visualization will always show the direction.

[UPDATED]

If you also want to include "floating" nodes that are not attached to a relationship in your relationship list, then you could just use a separate floating node ID list. For example:

MATCH p=()-[r]-()
WHERE ID(r) IN [11, 12, 13, 14]
RETURN p
UNION
MATCH p=(n)
WHERE ID(n) IN [6]
RETURN p

Upvotes: 1

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