You are correct in that your Interest objects are being re-added, because the copies held in your model are not being tracked by EF and therefore it thinks they are new. Instead, you will need to look up the versions from your repository, and add those instead.
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.