Add support for Neo4j based server entities.

[michael-simons]

This PR is a joint venture of @atomfrede and the Neo4j SDN-RX team. It brings a first work in progress of Neo4j integration with JHipster through Neo4j SDN-RX (Find the project here https://github.com/neo4j/sdn-rx and a description here https://medium.com/neo4j/spring-data-neo4j-rx-beta-iii-79573a773584).

The solution proposed in this PR stems directly from the discussion in #9967.

In the box is

• support for Neo4j based entities and repositories
• support for reactive repositories with Neo4j 4.0
• Neo4j migrations (Flyway like db migration approach)
• storage for the user and roles inside Neo4j if applicable

I missed the RFCs, so there's not a formal RFC, but I'm trying to recap this here:

Summary

This features adds support for Neo4j based on Spring Data Neo4j / RX.
The support includes Neo4j driver and client beans to access Neo4j without repositories as well as support for storing user information and entities through the common Spring Data repository abstraction.

Motivation

We are doing this to provide a different No-SQL solution for staring data, in form of Graphs. JHipster users will be able to benefit from a Graph database, Neo4j practitioners will be able to delegate all the CRUD cruft to the much appreciated and elegant solution of a generator like JHipster together with SDN/RX.

It doesn't add new concepts.

• All continuous integration tests are green
• Tests are added where necessary
• Documentation is added/updated where necessary
• Coding Rules & Commit Guidelines as per our CONTRIBUTING.md document are followed

Documentation and support for JDL has been provided by these two PRs:

jhipster/jhipster.github.io#889

jhipster/jhipster-core#428

[atomfrede]

Thanks @michael-simons for the work! As we have discussed it in the issue I think a RFC was not needed.

[atomfrede]

Not sure why all mongo db tests are failing, seems unrelated 🤔

[atomfrede]

Okay looks like breaking mongo builds are in fact related as they seem to work for other PRs from this morning. Will try to have look later or tomorrow on the 🚄

[atomfrede]

🎉 Yeha, all tests are green!

[atomfrede]

@jhipster/developers How should we proceed with the dependencies here? So we would need to update the jhipster bom to 3.4.0 here and streamline the generated pom (dependency versions). We need to merge and release jhipster/jhipster-core#428 to have jdl support. An open question is how to integrate neo into cour ci? Do we have some capacity left for github actions? How to integrate it into our nightly/daily builds? I think it can be done after we have it released, right?

[pascalgrimaud]

@atomfrede :

• about jhipster bom 3.4.0, our CI uses the master version, so it's ok (see https://github.com/jhipster/generator-jhipster/blob/master/.github/workflows/angular.yml#L25-L26)
• if you need a release of jhipster lib, I can do one, just tell me
• for jhipster-core release, what do you think @MathieuAA ?
• MySQL is tested several time, we can replace 2 builds (1 in Angular and 1 in React) and use Neo4J instead
• for daily builds, no problem, it can be added later

[MathieuAA]

I can do one tomorrow, no problem.

[pascalgrimaud]

There are some conflicts, can you resolve it plz ?

[MathieuAA]

By the way, feel free to merge your PR in JCore @atomfrede. I can do it tomorrow too if you give me the go

[atomfrede]

There are some conflicts, can you resolve it plz ?

Sure, will have a look this evening.

I would say let's do it like this:

• Merge and release JHCore
• Merge this PR
• Update main generator with latest JHCore (and bom)
• Replace react + mysql with neo4j + angular
• Add it to daily builds (already prepared a PR)

What can come later:

• Update documentation (WIP PR is there)
• Integrate into kotlin blueprint

what do you think?

[MathieuAA]

JCore's V7 is released

[atomfrede]

@MathieuAA thanks!

[michael-simons]

Awesome and so far, thank's to everyone involved. Again, hat-tip to @atomfrede for working his way through our new Spring Data integration! Your feedback and test was super valuable.

We are currently writing the manual, should be finished by the end of the month, early March:
https://github.com/neo4j/sdn-rx

[atomfrede]

Bounty claimed https://opencollective.com/generator-jhipster/expenses/14484

[pascalgrimaud]

@atomfrede : just approuved