I'm trying to write microservices in Java. I've implemented GraphQL endpoints using graphql-spring-boot-starter.
Now I have a problem how to make it efficient.
Datamodel is like a tree and I need to query for data from multiple services at once. The problem is how to filter for a member of collection, something like CONTAINS in database, but data is not in separate table, but separate microservice. Maybe the problem is that domain is not correctly splitted between services?
Let's make an example: I have 3 microservices: users, libriaries, books. Every library have collection of users and books (just list of identifiers, like foreign keys). Every book has a name and genre. Every library have lists of books borrowed by user (identifiers too).
Question 1 - should library hosts list of books and users (just identifiers, like foreign keys)? Is it correct approach?
Question 2 - I want to find libraries in which specified users (by surname) have borrowed books of specified genre. Going from top I need to first find libraries containing users. Not easy, as we have names in different service. We need to query first for users, gathers their identifiers, and now we are able to query for libraries. But it isn't all. Now we need to find books for every user and check genres - in different service. And it's not all. I want to have everything presented in nice way, so whole output should be sorted and paged. It force me to collect all data from all services, then page and sort it, which of course will not be efficient.
Please don't concentrate on this example, I'm looking how to solve general approach, not this one example. I've tried to use Datafetchers but it's troublesome and there are not good examples of calling Graphql-to-GraphQL. Most examples covers calling REST endpoints etc.