Neo4j: Cypher Query With Variable Length and Condition on Node Labels

Question

What I'm looking for

With variable length relationships (see here in the neo4j manual), it is possible to have a variable number of relationships with a certain label between two nodes.

# Cypher
match (g1:Group)-[:sub_group*]->(g2:Group) return g1, g2

I'm looking for the same thing with nodes, i.e. a way to query for two nodes with a variable number of nodes in between, but with a label condition on the nodes rather than the relationships:

# Looking for something like this in Cypher:
match (g1:Group)-->(:Group*)-->(g2:Group) return g1, g2

Example

I would use this mechanism, for example, to find all (direct or indirect) members of a group within a group structure.

# Looking for somthing like this in Cypher:
match (group:Group)-->(:Group*)-->(member:User) return member

Take, for example, this structure:

group1:Group
   |-------> group2:Group -------> user1:User
   |-------> group3:Group
                  |--------> page1:Page -----> group4:Group -----> user2:User

In this example, user1 is a member of group1 and group2, but user2 is only member of group4, not member of the other groups, because a non-Group labeled node is in between.

Abstraction

A more abstract pattern would be a kind of repeat operator |...|* in Cypher:

# Looking for repeat operator in Cypher:
match (g1:Group)|-[:is_subgroup_of]->(:Group)|*-[:is_member_of]->(member:User) 
return member

Does anyone know of such a repeat operator? Thanks!

fiedl fiedl · Accepted Answer · 2015-04-20T18:41:16

Possible Solution

One solution I've found, is to use a condition on the nodes using where, but I hope, there is a better (and shorter) soluation out there!

# Cypher
match path = (member:User)<-[*]-(g:Group{id:1}) 
where all(node in tail(nodes(path)) where ('Group' in labels(node))) 
return member

Explanation

In the above query, all(node in tail(nodes(path)) where ('Group' in labels(node))) is one single where condition, which consists of the following key parts:

all: ALL(x in coll where pred): TRUE if pred is TRUE for all values in coll
nodes(path): NODES(path): Returns the nodes in path
tail(): TAIL(coll): coll except first element–––I'm using this, because the first node is a User, not a Group.

Reference

See Cypher Cheat Sheet.