[TYPO3-mvc] General question about relations in extbase

[hacksaw at zpeed.dk]

Hello

This is a newbie question, but I simply can't find any helpful material on
Google (I'm probably using the wrong search terms).

I'm new to the MVC concept, have been coding procedural style for way too
long.

I have used "Extension Builder" to build a complex model of an extension I
want to make. It's an extension for FE users to login and make
registrations of certain things.

So I a model object of employees with a 1:1 relation to the class:
TYPO3\CMS\Extbase\Domain\Model\FrontendUser (This works, although I felt
it necessary to change the TCA, so it didn't use inline, but select.)

Next comes a model object of registrations the employee has made.

Where should I put the relation and why?
If I place the relation in the employee object, how do I retrieve the
employee of a specific registration?
The registration will be "attached" to the employee and in the backend I
will be able to see all the registrations made by an employee. But I will
not be able to see the employee on the registration itself.

Yet, if I place the relation on the registration (which is what I would
normally do in a pibase extension), how do I retrieve all the
registrations made by an employee?

Can someone point me to some material I can read to get a better
understanding of this?