Anyone custom coded a component to allow this?

Basically I have a film component which has a field called GENRE which links via FK to table called (wait for it) Genres.

A movie can have more than one genre so I need a multselect box with data from an FK

I know the builder itself cant do this, but has anyone successfully converted a component to allow a multiselect field?

Thanks in advance for any tips. I can think of many approaches, but one that is tried and tested and working will be awesome!

Any one done this? Cook? Is this possible with the currnet framework in some way.. JSON field maybe with a bit of custom code on the front end?

I think the Joomla component docs give some examples, but would rather use the existing framework rather than have fields of different types

Better to use N:M than JSON
N:M is not ready yet, so I prefer not to provide 'official' example for not creating more confusion, but I remember some topics about that.

I am working on that feature (N:M), but it is not ready yet because I had preferred to focus on FOF before. N:M is the next coming.