Create dynamic drop down of subject list in book's create form, using Rails 4.0 and Ruby 2.2

I have two model Subject and Book, and the association between them is subject has_many books and book belongs_to subject. Now I need to have drop down in book's form for subject where only those subject which got created by current user should display in drop down. Please suggest or provide me the link if any possible solutions are available.

Thanks in advance