library

Controllers

Today's homework is going to focus on controllers.

Things to know for this homework:

• Views are a new concept that you will be learning about in greater detail during tomorrow's homework. For now, just know that they have access to instance variables defined by the corresponding controller action (e.g. the books' index view has access to instance variables defined in BooksController#index) and are what we actually see on the page.
• In the videos/readings on controllers so far, we have seen them render :json; for this assignment, we will be rendering templates instead. For example, to render the index, we simply render :index. To redirect to the index, we redirect_to the url that matches our intended route when we rails routes – in this case, the books_url.

A basic rails project has already been made for you - except for the controllers. Download the skeleton zip. To set up, navigate into the project directory and run:

bundle install
bundle exec rails db:setup
rails s

Now we have some basic data and our server is running and ready to take requests.

Index and Destroy

The app has a basic library of books. Right now, we only have routes to see the list of all books (:index) and delete (:destroy) whichever books we like; we can see that these are the only options available to us by checking our routes.rb file in the config folder:

Rails.application.routes.draw do
  resources :books, only: [:index, :destroy]
end

Check those out by navigating to localhost:3000/books. Whoops! We get this error:

Our books' index view is expecting there to be a @books variable that contains all the books from the database, but it's currently nil. This is a job for our controller's index action! Get your index working so that @books is correctly set to all books and we can see our library's index page.

Now we can see our awesome library of books, but how about deleting them? Try one of those delete buttons and you'll notice another error: Missing template. Rails is automatically searching for our destroy template. But we actually don't need one! We don't want to render a delete page -- we just want to update the index page so that our deleted book is no longer showing.

When we hit the 'delete' button, it hits our controller's destroy action. Using ActiveRecord, find the book in question, delete it, and redirect_to the index page. This redirect will override the default search for a destroy template. Hint: the controller has access to the params that are passed through as part of the request. Because we have the binding_of_caller and better_errors gems installed (as part of the gemfile), you can throw a fail in to your destroy action, try to delete a book, and use the console that appears in the browser to see exactly what the params look like. What param will we use to find the correct book in our ActiveRecord query?

New and Create

Delete some books. You'll notice that our library is shrinking, but there's no way to add new books to our collection (that 'add a book' link down at the bottom isn't working!). Let's add that functionality. To do this, we need corresponding routes that will 1) give us the form to add a book (already made for you!) and 2) save that new book to the database (:new and :create, respectively). Let's update our routes.rb file to reflect this. It should look like this:

Rails.application.routes.draw do
  resources :books, only: [:new, :create, :index, :destroy]
end

Now we can check our existing routes by running bundle exec rake routes in the terminal. We have these :new and :create routes now, and they are expecting the corresponding controller actions to work properly when we navigate to them. Let's finish up by writing those new and create controller actions! The new action's job is just to render the page with the form to add a book; create is what will actually save that new book with the parameters we give it to the database.

Hints:

• the new template has already been made for you and is located at app/views/books/new.html.erb
• the create action needs to redirect_to the index page if we want to see our new book added to the library
• you can hit the :new route by either clicking on the 'Add a book!' link or navigating directly to localhost:3000/books/new
• our create action has access to the values submitted through the new book form via the private book_params method provided for you in the BooksController

Feeling stuck? Revisit the RESTful Controller Demo and additional readings!

Once you've got it working, celebrate by adding some of your favorite books! 📚