I am trying to achieve many to many relationship between two custom Post Types. This is exactly my problem: many to many, but the solution seems to be very complicated, and actually I can't manage to run it properly. I would like to write as simple solution as possible and achieve this:

Custom Post Types: Movies and Actors.

I would like to choose Actor trough Metabox while creating Movie. I would like also to choose Movie trough Metabox while creating Actor.

I know that there isn't any native solution for that (or maybe is?). What are the necessary parts only to run it properly?

I don't want to use any third party plugins.

Thx!