限制关系中公共节点的数量-Neo4j

Question

Say I have a nodes person and movie with a relation of [likes]. I am trying to be able to limit the amount of persons that like the same movie without limiting my results to only include 1 movie.

For example:

    MATCH (p:Person)-[LIKES]->(m:Movie)
    WHERE
    p.age < 30
    p.gender = "Male"
    RETURN p,m

So in the query above I would like to get all the results but filter them so that only 2 Persons will like the same movie.

Is this possible?

Answer 1

This knowledge base article goes over different ways to limit match results per row .

For a non-APOC approach you can get the slice of the collection of people who liked the movie:

MATCH (p:Person)-[:LIKES]->(m:Movie)
WHERE
p.age < 30
p.gender = "Male"
RETURN m, collect(p)[..2] as peopleWhoLiked

If you want a separate row per person, then UNWIND the peopleWhoLiked list before the return.

For the second approach, you'll need APOC Procedures.

In order to use LIMIT, you'll need to first match on all movies, then perform the limited match to :Person nodes using apoc.cypher.run() .

Answer 2

To get all movies that have exactly two (under-30 male) likers:

MATCH (p:Person)-[:LIKES]->(m:Movie)
WHERE
  p.age < 30 AND
  p.gender = "Male"
WITH m, COLLECT(p) AS likers
WHERE SIZE(likers) = 2
RETURN m, likers;