add an IsAdmin attribute to the current Student model
Create Assignment/new and index page, create assignment_controller
creat is_admin method in application_controller
create show.html.erb to show current student assignment, fix login as an admin user, Add a link to user's assignment for students
Prevent students to view other's grades if they change the URL
generate upload_controller
Add upload resources to routes file
rollback and destroy upload_controller
Add Assignments/upload page, Create upload assignment button in All assignments page
Create upload.html, Add upload routes to routes.rb file
prevent unauthorized users from uploading assignments
Re-generate import model and imports_controller, Add /imports/index file to upload assignments, delete unnecessary codes, add imports to the routes file
fix code typos and some indentation mistakes