CODEWITHSUNDEEP
neo4jgraph-databases
Rudie
Rudie

Reputation: 53881

Graphdb/Neo4j relationship to another relationship, or relationship with 3 nodes

I want to make IMDB's characters/roles structure in Neo4j. I'll need labels Person, Movie and Character. Character, because a character can be in multiple movies, played by different people.

Without Character, it's easy:

(Person)-[:PLAYS_IN]->(Movie)

But PLAYS_IN is a Character, so it would be something like:

(Person)-[:PLAYS_AS]->(Character)-[:PLAYS_IN]->(Movie)

but that doesn't work, because it doesn't have a direct Person-Movie relationship. Without that, everyone who ever played Peter Parker, is in every movie that has a Peter Parker.

There must be a Person-Movie relationship, but also a Person-Movie-Character relationship. How? This could work, but that's just nasty:

(Person)-[:PLAYS_IN {uuid}]->(Movie), (Character {uuid})

because now I'm creating my own foreign key kind of relationship. That's very ungraphdb. But it works:

MATCH (p:Person)-[r:PLAYS_IN]->(m:Movie), (c:Character)
WHERE c.uuid = r.uuid
RETURN p, c, m

by building a cartesian product =( which is very RDBMS, but not very graphdb. And I can't query Character-Movie or Character-Person, because that's not a real relationship.

How do I make a RDBMS link table with 3 foreign keys (movie_id, character_id, person_id) in Neo4j??

edit 1
The RDBMS equivalent:

movies (id, title)                         # e.g. Dragon Tattoo, or Spider's Web
people (id, name)                          # e.g. Rooney Mara, or Claire Foy
characters (id, name)                      # e.g. Lisbeth Salander
roles (movie_id, person_id, character_id)  # 2 rows with 1 distinct character_id

Upvotes: 2

Views: 270

Answers (2)

stdob--
stdob--

Reputation: 29167

Your problem is solved by hypergraphs. But since neo4j does not support hypergraphs, you need to model them. For example:

CREATE (P1:Person {name: 'Tobey Maguire'})
CREATE (P2:Person {name: 'Nicholas Hammond'})
CREATE (CW1:CreativeWork {name: 'Spider-Man'})
CREATE (CW2:CreativeWork {name: 'The Amazing Spider-Man (TV Series)'})
CREATE (CH:Character {name: 'Spider-Man'})

CREATE (A1:Role)
CREATE (A2:Role)

CREATE (P1)-[:PLAYS_AS]->(A1)
CREATE (A1)-[:HAS_CHARACTER]->(CH)
CREATE (A1)-[:PLAYS_IN]->(CW1)

CREATE (P2)-[:PLAYS_AS]->(A2)
CREATE (A2)-[:HAS_CHARACTER]->(CH)
CREATE (A2)-[:PLAYS_IN]->(CW2)

enter image description here

Upvotes: 3

ThirstForKnowledge
ThirstForKnowledge

Reputation: 1304

Make your relationship between Actor and Movie a rich relationship, where an Actor who PLAYED_IN a Movie plays a specific Role. The Role is implemented as a separate entity (relationship entity) with its own properties and only becomes an entity when the relationship between Actor and Movie exists.

@NodeEntity
public class Actor {
    Long id;
    @Relationship(type="PLAYED_IN") private Role playedIn;
}

@RelationshipEntity(type = "PLAYED_IN")
public class Role {
    @Id @GeneratedValue   private Long relationshipId;
    @Property  private String title;
    @StartNode private Actor actor;
    @EndNode   private Movie movie;
}

@NodeEntity
public class Movie {
    private Long id;
    private String title;
}

(token from the mentioned link)

Upvotes: 1

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