I believe you can set the relationship to null from the other side as in
door.car = null;
You can read more about this here: https://wiki.mezzanineware.com/display/HTUT/Lesson+6%3A+Relationships
If I want to remove the relationship between two objects with @ManyToOne, is the only way to do car.doors.remove(i) where i is the position of the item to be “unlinked”?
I believe you can set the relationship to null from the other side as in
door.car = null;
You can read more about this here: https://wiki.mezzanineware.com/display/HTUT/Lesson+6%3A+Relationships