cakephp controller save from scaffolded “join table” relationship, non-conventional primary keys

When I build interfaces on top of a pre-established database schema, I usually can’t change schema properties.  That’s a problem when working with a “convention over configuration” MVC Framework like cakephp. After baking/scaffolding a CRUD interface based on a “join table” (HABTM) class, that issue came into focus, once again.  I have had run into…