Distinguish models

I have three models:

Applications, Permission, User

And for Application I have

has_many :permissions, :through => app_default
has_many :permissions, :through => app_perm

Will that work? If I开发者_运维知识库 do Application.permission from which table will take the permissions? What about nested forms as well?

---

Use polymorhpic associations to get this work.