Returning only simple paths in Neo4j Cypher query

问题:

Given a query like the following:

START n = node(123)
MATCH p = n-[r:LIKES*..3]->x
RETURN p;

The result paths that I get with the query above contain cycles.

How can I return only simple paths?

Given this example:

• How can I avoid paths with repeated nodes like: [Neo, Morpheus, Trinity, Morpheus, Neo]

回答1:

Specifying the uniqueness of paths is a planned feature of cypher.

So right now we have to ascertain that no node is a duplicate in the path.

There is an ALL predicate that must hold true for all elements of a collection (which a path is). And with filter you can extract the elements of an collection for that a certain condition holds true.

START neo=node(1) 
MATCH path= neo-[r:KNOWS*..4]->other 
WHERE ALL(n in nodes(path) where 
          1=length(filter(m in nodes(path) : m=n))) 
RETURN neo, LENGTH(path) AS length, EXTRACT(p in NODES(path) : p.name), other 
ORDER BY length

So what I did was:

• For all nodes of the path n
• Filter the path for the nodes that are equal to n
• determine the length of that collection
• assert with ALL that it has to be ONE for each n

see: http://console.neo4j.org/r/dpalbl

回答2:

my workaround for this:

START n = node(123), x=node(*)
MATCH p = shortestPath(n-[r:LIKES*..3]->x)
RETURN p;

see the example in console

回答3:

In 2.3.0, use the following:

MATCH path = (start {id:2})<-[*1..]-(end {id:3}) 
WHERE ALL(n in nodes(path) where 
          1 = size(filter(m in nodes(path) where m=n))) 
RETURN start, LENGTH(path) AS length, EXTRACT(p in NODES(path) | p.id), end
ORDER BY length