I'm trying tocreate a constraint on a relationship without succeding

Neo4j Graph Platform Cypher
,
1
  • neo4j 5.26.7 EE, desktop version 2.0, browser version

Well,

I have a relationship p = ()-[h:HAS_TAG]->(r:name)

let me show you what i want to achieve:

  1. p = (n:Node)-[h:HAS_TAG]->(t1:TAG { name : "Donald" }) // which is formally CORRECT
  2. p = (n:DifferentNode)-[r:HAS_TAG]->(t1:TAG { name : "Duck" }) // which is formally CORRECT, because I want to allow different nodes to have the same attribute.name
  3. p = (n:Node)-[h:HAS_TAG]->(t1:TAG { name : "Trump" }) // which is WRONG, because I don't want to allow the same node to have more than one attribute with the same name

My constraint is:
CREATE CONSTRAINT IF NOT EXISTS FOR ()-[r:HAS_TAG]->(t:Tag) REQUIRE t.name IS UNIQUE ON r;

where I mean that Tag attributes must be unique on the relationship r
but it returns an error which for some reasons, is not as some notices I found on the documentation;

2

The documentation I've found doesn't mention "relationship existence constraints", the constraints it shows are only on properties on a node or on a relationship, can you point me at the documentation you used?

3

There is no constraint where you can specify a relationship and related nodes. The constraints are defined a node or a relationship, not a combination of the two. What you want to do is not available.

4

A possible way to emulate the behaviour you want with the constraints as they are:

CREATE CONSTRAINT IF NOT EXISTS FOR ()-[r:hasTag]->() REQUIRE r.tagName IS UNIQUE

Your tagName is the unique identifier of :Node + the property you want to be unique:

CREATE (A:Node {uuid: $nodeUuid })-[:hasTag {tagName: $nodeUuid + 'name'}]->(B:TAG {name:'4'})

For any node :Node, only 1 property with a specified property name exists.

5

Well, it could be a good idea or suggestion for the future!