Finding leaf nodes in a Neo4J database

Question

We have a project where we use Spring Data Neo4J. One of the important entities is shown below: ``` @NodeEntity public class Category { @GraphId Long id; String name; @RelatedTo(direction = Direction.INCOMING, type = "CHILD") Category parent; @RelatedTo(direction = Direction.OUTGOING, type = "CHILD") Set<Category> children; } ``` We have a requirement to find out all the leaf categories (that is, categories without any children) starting from a specific category whose name is known. For example, given the hierarchy shown below: ``` Electronics Camera Point and Shoot SLR Computing Desktop Laptop Tablet Netbook Furniture Tables Office tables Home tables Chairs Lounge chairs Office chairs ``` a search for "Furniture" should return "Office tables", "Home tables", "Lounge chairs" and "Office chairs". Similarly, a search for "Computing" should return "Desktop", "Laptop", "Tablet" and "Netbook". Need help in creating a cypher query that can be placed on a Spring Data repository method to giv…

Accepted Answer

This is the simplest way I've found with cypher: http://console.neo4j.org/r/cgrndo

```
start n=node(*) // you can specify a single node here if you want
match n-[r*]->m
where not(m-->()) // this limits m to be only leaf nodes 
return distinct m; // this returns the distinct leaf nodes (not necessary if there are only simple paths)
```

Edit: (since people are recently upvoting this... here's an update using 3.x cypher)

```
match (n) 
where not (n)-->() 
return distinct n
```

Finding leaf nodes in a Neo4J database

Solution

Problem