Should I use MongoDB with entity's relations to be non-blocking end to end with my Spring 5 project?

Question

I started a Spring WebFlux project some times ago, the goal of this project is to offer an REST API which collects its data from a database.

I currently go with a reactive approach thanks Reactor project included inside Spring 5 release and created reactive controllers. I need to persist in my database normalized datas with relations, this is why I use PostgreSQL.

At the time I am writing this lines, no reactive programming support is provided for JDBC and so JPA. But my controllers are only truly non-blocking if other components that they work with are also non-blocking. If I write Spring WebFlux controllers that still depend on blocking repositories, then my reactive controllers will be blocked waiting for them to produce data.

I would like to be non-blocking end to end, so I wonder to move on one of the NoSQL databases supported by Spring Data : Cassandra DB or MongoDB. I don't think Cassandra DB really fits to my needs, I will need to rewrite my entities and think differently my database's structure to be query oriented.

I read it is possible to keep some relations between my entities with MongoDB, especially with the last 4.0 version without refractor completely my db schema. But I wonder what is worth ?

• Switch to MongoDB even if I need to keep relational datas
• Keep to fetch data in a blocking fashion and then translate it into a reactive type as soon as possible
• Forget Spring WebFlux and go back to Spring MVC (probably not)

Thank you for any help and advice !

Answer 1

I think it depends on your context, it seems that moving to a document db might not be a good fit for your data as it seems fully relational unless you are sure you can model your data as a bunch of aggreates, otherwise you might end up having other problems such as transaction consistency when checking consistency rules between your models. As a first option i would try to fetch data in another thread, perhaps wrapping the call in an rxjava observable. Although it is still a blocking call it will not block the main thread and you will be able to make better use of resources.

Those are my 2 cents. Regards