Persisting relationships with properties with Spring Data Neo4J

Drivers & Stacks Spring Data Neo4j & Neo4j-OGM
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1

Hi all, I have a conceptual question in terms of persisting relationships with properties. I've googled and seems @RelationshipEntity is the way to go, however all references I've seen of it come from the OGM dependency (like "org.neo4j.ogm.annotation" for example).

Is there a way to achieve this by using SDN? I wouldn't assume this is the way; I've heard the new SDN version is isolated from OGM. Or maybe my assumption is not correct?

2

Quick recap:
SDN 5 and lower use Neo4j-OGM as the mapping framework
SDN 6 is a standalone solution without Neo4j-OGM

From what we have learned with RelationshipEntity also from the user perspective, we decided to downgrade relationships with properties from a first class entity to a rich connection between @Node entities.
This means that we still support relationship with properties (SDN 6 documentation - Relationship properties) but you cannot work with them directly and have to use the relationship defining entities (nodes) to load, modify and persist them.

3

Thank you, this completely clears the questions I had.

4

Hi, I have the same question but the answer is not very clear to me. How to use the relationship defining entities (nodes) to load, modify and persist relationship properties exactly? The documentation mentions @RelationshipProperties is the way but doing that doesn't create any relationships at all. Same issue here by another user: java - Relationship not saved in SDN 6 (Spring data neo4j) - Stack Overflow

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Finally, I discovered that the issue with persisting relationship properties using @RelationshipProperty annotated class is due to the implicit conversion between long and Long. Changing @RelationshipId private long id; to @RelationshipId private Long id; inside the @RelationshipProperty annotated class will do the trick. This appears to be a bug in SDN, it should report an error instead.

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@gerrit.meier

"...but you cannot work with them directly and have to use the relationship defining entities (nodes) to load, modify and persist them"

Could you share an example per your comment. We have a huge migration of codes based on RelationEntity from our platform. And with the new changes to 5, it is a huge blocker. It would be great to see an example on retrieving/updating a relationship properties.

Also could you please address three questions we have:

  1. Base on the documentation for relationship, are we only allow to store int values for relationship
  2. What is the reasoning for dropping it. I have not read one clear reason why it was moved away from first class entity.
  3. Do you think it is best that we completely not store any values in our relationship in the future as you guys already dropped non-int value for relationships.

Please feel free to clear any of my assumptions.

Thanks in advance

7
  1. No, you can store any Neo4j Java Driver supported property type or converter-enabled type (Supported types - SDN reference)
  2. Spring Data as a whole has a concept of entities and associations. Nodes are definitely the entities and (non-entity based) relationships are associations, no doubt. The, not so easy, decision to make also relationship properties / relationship entities "just" associations was taken to align Spring Data Neo4j more to the general Spring Data idea, and, last but not least, benefit from the built-in support for associations and general "object navigation" in the shared based Spring Data (commons) library.
    This is also important for future development to not move SDN into a different direction than the other Spring Data modules develop and suddenly run into conflicting behaviour.
  3. see 1.
8

Thanks for answering.

We are still looking for an example to retrieve single relationship and update relationship. We originally saved relationship with @RelationEntity. Currently, we are not able to save relationship with @RelationshipProperties. Can you share an example how/where we can integrate with the latest SDN?