CODEWITHSUNDEEP
neo4jcyphergraph-databases
sthzg
sthzg

Reputation: 5554

Cypher: Ordering Nodes on Same Level by Property on Relationship

I am new to Neo4j and currently playing with this tree structure:

enter image description here

The numbers in the yellow boxes are a property named order on the relationship CHILD_OF.

My goal was

a) to manage the sorting order of nodes at the same level through this property rather than through directed relationships (like e.g. LEFT, RIGHT or IS_NEXT_SIBLING, etc.).

b) being able to use plain integers instead of complete paths for the order property (i.e. not maintaining sth. like 0001.0001.0002).

I can't however find the right hint on how or if it is possible to recursively query the graph so that it keeps returning the nodes depth-first but for the sorting at each level consider the order property on the relationship.

I expect that if it is possible it might include matching the complete path iterating over it with the collection utilities of Cypher, but I am not even close enough to post some good starting point.

Question

What I'd expect from answers to this question is not necessarily a solution, but a hint on whether this is a bad approach that would perform badly anyways. In terms of Cypher I am interested if there is a practical solution to this.

I have a general idea on how I would tackle it as a Neo4j server plugin with the Java traversal or core api (which doesn't mean that it would perform well, but that's another topic), so this question really targets the design and Cypher aspect.

Upvotes: 3

Views: 1478

Answers (1)

Michael Hunger
Michael Hunger

Reputation: 41676

This might work:

match path = (n:Root {id:9})-[:CHILD_OF*]->(m)
WITH path, extract(r in rels(path) | r.order) as orders
ORDER BY orders

if it complains about sorting arrays then computing a number where each digit (or two digits) are your order and order by that number

match path = (n:Root {id:9})-[:CHILD_OF*]->(m)
WITH path, reduce(a=1, r in rels(path) | a*10+r.order) as orders
ORDER BY orders

Upvotes: 1

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