The only way to do this is to explicitly store on the base model what type it is. So have a derived_type (or whatever) field on BaseMedium, and set it on save. Then you can have a get_derived_type method.
Thanks mr. Roseman for your reply. I developed your idea a bit further. Here is what I came up with.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.