c# - Convert Object to Inherited Object -

i working on program similar netflix , involves movies.

i have movie object/class api program uses. made inherited class of object so.

using system; using system.collections.generic; using system.linq; using system.text; using system.threading.tasks; using tmdblib.objects.movies; namespace movie_management.data {     class mymovie: tmdblib.objects.movies.movie     {         public string path { get; set; }     } } 

here code movie object api use.

        tmdblib.objects.movies.movie movie = new tmdblib.objects.movies.movie();         movie = movieprocesses.loadtmdblib(justmoviename);         mymovie mymovie = (mymovie)movie;         mymovie.path = path;          cacher cache = new cacher();         cache.cachevideo(mymovie); 

i attempt cast tmdblib movie mymovie object. not work. supposed in situation?

{"unable cast object of type 'tmdblib.objects.movies.movie' type 'movie_management.data.mymovie'."} 

you can't cast "backwards" in inheritance hierarchies. can go movie mymovie, not other way around.

if want add stuff existing movie object, add constructor mymovie takes movie object parameter , copy member variables across manually.