Hexagonal Architecture and relational database, how to connect it?

I am trying to use hexagonal architecture in my new project but I am a little bit confused about my connections between domain objects.

For example, I have User class, which is domain class. This class should be connected with Film class by one-to-many relation.

So I will create two different modules, first will be Users second will be Films.

How to use @OneToMany relationship from Hibernate in this situation without changing visibility scope of domain classes?

I am thinking about creating DTO's which are public and wire them together.

Do you know any example of usage hexagonal architecture with relational databases? I am only managed to find examples of no-SQL databases. How to use this approach with SQL databases in general?

In my project, I will use spring boot, hibernate and MySQL.

Thanks.