Creating a relationship to a relationship in Neo4j - neo4j

Question

Is it possible to create a relationship to a relationship in Neo4j?
The use-case goes something like this:
I have a bunch of questions, like "What movie should we see?"
Each question can have many options like "Movie1", "Movie2", etc.
For each question I want a user to be able to vote for their favorite option.
The graph would preferably look something like this:
(:Question {name:"What movie?"})-[:Option]->(:Movie {name:"Movie1"})
^
|
[:Vote]
|
(:User)
I realize that one way I could solve this is with the following:
(:Question)-[:Option]->(:Movie)<-[:Vote]-(:User)
But then if I decide to remove the Movie as an Option in the future, I don't get to take advantage of DETACH and will have to manage removing the Vote relationship myself. Not to mention, if the Movie belongs to multiple categories, I have to keep track of which Question->Movie relationship it belongs to (probably with some sort of ID). It just seems very messy...
Is is possible to create a relationship to a relationship? Or am I going to have to manually enforce referential integrity?

Answer 1

Is is possible to create a relationship to a relationship?
No. This is not possible. According the docs:
A relationship connects two nodes, and is guaranteed to have a valid
source and target node.
That is: the start and end point of a relationship should be a node.
I believe you should do some changes in your data model. For example:
Maybe the Option can be a node and not a relationship. Make more sense, not? This way:
(:Category)-[:HAS]->(:Option)
Also, the Vote can be a node too, and not a relationship... This way, when the user makes (a relationship, ahn?) a vote, this vote node will reference the option and the category that it is relative to.
(:Category)-[:HAS]->(:Option)
\ /
[:FOR_CATEGORY][:FOR_OPTION]
\ /
(:Vote)
|
[:MAKES]
|
(:User)
If, for example, you need to delete a Option and consequently the :Votes related to it you can do something like:
MATCH (o:Option {id:10})<-[:FOR_OPTION]-(v:Vote)
DETACH DELETE o
DETACH DELETE v
Make any sense? Sorry for my ASCII art. :)

Answer 2

I'm investigating this. The only reasonable way I can find is to assign an identifier to the relationship (:HAS in your case) and then use it in the pointing relationship (:VOTE).
Neo4j has internal IDs for this (see the ID() function), but I usually prefer to try to assign a semantically meaningful ID (like a person's national insurance number, a page URL or, in case of relations, the hash code of its concatenated endpoint's identifers).