Hi Neo4j followers and experts, I have been thinking about how to model entities with versions in Neo4j a few times, but never had opportunity to implement such a thing. Now I find myself in a project where every version of everything is relevant. It turns out that the actual structure needed for the version management is not trivial.
I feel that this is something that would occur in more applications, so I thing that it would be a good idea to come up with, and document, a design pattern for how to model different versions of entities in Neo4j. I would love to get ideas from anyone on this, especially if you have implemented something like this, but even if you just have ideas it would be great to hear them. If you are modeling a perfectly hierarchical structure of versioned entities (such as a VCS), you can copy-on-modify each modified entity and it's parent. Something like this: / v1: - foo/ v1: - foofile v1 - bazfile v1 - bar/ v1: - barfile v1 Change to foofile results in: / v2: - foo/ v2: - foofile v2 - bazfile v1 - bar/ v1: ... Getting a versioned entity would in this case start traversing from the root for the desired version, and thus find the correct version for the desired entity. Each entity node would also have a relationship to the node representing the previous version of that entity, forming a linked list of versions for each entity. For the root this would be used to find a specific version, before traversing out the deisred resource. It can also be used to compute differences between versions of an entity. But what about the case when the structure is an actual graph (as opposed to a tree), or for some other copying *all* relationships and properties would be too expensive. It could be possible to only add the diff to the new version node, but how do you model removal? For properties you could overwrite with a default value, or store a sentinel, but how to model that a relationship has been removed from version to another without copying all of them? Any ideas on how to model entity versions? Any comments on my draft structures? Any input is valuable! Let's nail a pattern for modeling versioning, and get it into the wiki. Thanks, -- Tobias Ivarsson <tobias.ivars...@neotechnology.com> Hacker, Neo Technology www.neotechnology.com Cellphone: +46 706 534857 _______________________________________________ Neo mailing list User@lists.neo4j.org https://lists.neo4j.org/mailman/listinfo/user
