Find path for N levels with repeating pattern of directional relationships in Neo4J

Question

I'm trying to use Neo4j to analyze relationships in a family tree. I've modeled it like so:

(p1:Person)-[:CHILD]->(f:Family)<-[:FATHER|MOTHER]-(p2)

I know I could have left out the family label and just had children connected to each parent, but that's not practical for my purposes. Here's an example of my graph and the black line is the path I want it to generate:

I can query for it with

MATCH p=(n {personID:3})-[:CHILD]->()<-[:FATHER|MOTHER]-()-[:CHILD]->()<-[:FATHER|MOTHER]-()-[:CHILD]->()<-[:FATHER|MOTHER]-() RETURN p

but there's a repeating pattern to the relationships. Could I do something like:

MATCH p=(n {personID:3})(-[:CHILD]->()<-[:FATHER|MOTHER]-())* RETURN p

where the * means repeat the :CHILD then :FATHER|MOTHER relationships, with the directions being different? Obviously if the relationships were all the same direction, I could use

-[:CHILD|FATHER|MOTHER*]->

I want to be able to query it from Person #3 all the way to the top of the graph like a pedigree chart, but also be specific about how many levels if needed (like 3 generations, as opposed to end-of-line).

Another issue I'm having with this, is if I don't put directions on the relationships like -[:CHILD|FATHER|MOTHER*]-, then it will start at Person #3, and go both in the direction I want (alternating arrows), but also descend back down the chain finding all the other "cousins, aunts, uncles, etc.".

Any seasoned Cypher experts that an help me?

Answer 1

I am just on the same problem. And I found out that the APOC Expand path procedures are just accomplishing what you/we want.

Applied to your example, you could use apoc.path.subgraphNodes to get all ancestors of Person #3:

MATCH (p1:Person {personId:3})
CALL apoc.path.subgraphNodes(p1, {
    sequence: '>Person,CHILD>,Family,<MOTHER|<FATHER'
}) YIELD node
RETURN node

Or if you want only ancestors up to the 3 generations from start person, add maxLevel: 6 to config (as one generation is defined by 2 relationships, 3 generations are 6 levels):

MATCH (p1:Person {personId:3})
CALL apoc.path.subgraphNodes(p1, {
    sequence: '>Person,CHILD>,Family,<MOTHER|<FATHER',
    maxLevel: 6
}) YIELD node
RETURN node

And if you want only ancestors of 3rd generation, i.e. only great-grandparents, you can also specify minLevel (using apoc.path.expandConfig):

MATCH (p1:Person {personId:3})
CALL apoc.path.expandConfig(p1, {
    sequence: '>Person,CHILD>,Family,<MOTHER|<FATHER',
    minLevel: 6,
    maxLevel: 6
}) YIELD path
WITH last(nodes(path)) AS person
RETURN person

Answer 2

You could reverse the directionality of the CHILD relationships in your model, as in:

(p1:Person)<-[:CHILD]-(f:Family)<-[:FATHER|MOTHER]-(p2)

This way, you can use a simple -[:CHILD|FATHER|MOTHER*]-> pattern in your queries.

Reversing the directionality is actually intuitive as well, since you can then more naturally visualize the graph as a family tree, with all the arrows flowing "downwards" from ancestors to descendants.

Answer 3

Yeah, that's an interesting case. I'm pretty sure (though I'm open to correction) that this is just not possible. Would it be possible for you to have and maintain both? You could have a simple cypher query create the extra relationships:

MATCH (parent)-[:MOTHER|FATHER]->()<-[:CHILD]-(child)
CREATE (child)-[:CHILD_OF]->parent

Answer 4

Ok, so here's a thought:

MATCH path=(child:Person {personID: 3})-[:CHILD|FATHER|MOTHER*]-(ancestor:Person),
WHERE ancestor-[:MOTHER|FATHER]->()
RETURN path

Normally I'd use a second clause in the MATCH like this:

MATCH
  path=(child:Person {personID: 3})-[:CHILD|FATHER|MOTHER*]-(ancestor:Person),
  ancestor-[:MOTHER|FATHER]->()
RETURN path

But Neo4j (at least by default, I think) doesn't traverse back through the path. Maybe comma-separating would be fine and this would be a problem:

MATCH path=(child:Person {personID: 3})-[:CHILD|FATHER|MOTHER]-(ancestor:Person)-[:MOTHER|FATHER]->()

I'm curious to know what you find!