Let’s start by looking at your application’s routes again.

1. Open Terminal and go to your bookstore directory.

2. Run rake routes.

   So far we’ve worked with the first row in the routes table. We used the /books path with the BooksController index action to list all your application’s books.

   books GET    /books(.:format)          books#index
   

   Now that we want to show detailed book information we’ll need to use a different route.

   book GET    /books/:id(.:format)      books#show
   

   This time, we’ll use the /books/:id path with the BooksController show action to show a book’s information.

In the /books/:id path, we can take advantage of :id to get a book by it’s id.

What’s that? You didn’t know a book could have an id? Let’s take a look.

1. Go back to Terminal and start rails console.

2. In the console, run Book.first to get the first book from your database.

   Take a look at the output. It might be hard to see, but at the beginning there’s an id.

   #<Book id: 1, title: "why's (poignant) Guide to Ruby", ... >
   

   The first book in your database has an id of 1.

3. I wonder what id your second book will have…

   Run Book.second and look at the output.

   #<Book id: 2, title: "Oh, the Places You'll Go!", ... >
   

   The second book in your database has an id of … 2!!!

   By default, every book you create will be given a unique id, and it will be given an id in sequential order.

4. Exit the console.

How will the /books/:id path work in action?

1. Go back to Terminal and start your application’s web server by running rails server.

2. :id can be replaced with specific ids. Since we know your first book’s id is 1, we can go to /books/1.

   Open your browser and go to http://localhost:3000/books/1.

3. An unknown action error?! Why does that look familiar… 😉

   You’re trying to access the BooksController show action, but it doesn’t exist. Let’s make it!

1. Open your text editor and go to app/controllers/books_controller.rb.

2. After the index action, add the following:

   def show
   end
   

3. Save your changes, and go to http://localhost:3000/books/1 again.

4. Now you get a different error:

   ActionController::UnknownFormat (BooksController#show is missing a template for this request format and variant.
   

   We’ve seen this error too. You added the show action, but it doesn’t have a template to go with it.

Let’s add the missing template.

1. Go back to Terminal and stop your application’s web server by running Ctrl-C.

2. Now, run touch app/views/books/show.html.erb to create the empty template.

3. Restart your application’s web server by running rails server and revisit http://localhost:3000/books/1.

   Remember, a blank page means no errors. 😆

   Now that we have the BooksController show action rendering a template, we’re ready to show a book’s details.

1. Open your text editor and go to app/controllers/books_controller.rb.

2. Request parameters are available in all your application’s controllers as params.

   Inside the show method, add the following code:

   @id = params[:id]
   

By defining @id in the BooksController show method, it’s available in the BooksController show template.

1. Open app/views/books/show.html.erb in your text editor and add the following:

   This book's id is <%= @id %>.
   

2. Save your changes.

Now that the BooksController show template is wired up to render something, what do you expect to see if you visit http://localhost:3000/books/1?

Do you have an idea? Let’s verify it!

1. Go to http://localhost:3000/books/1.

   What do you see?? Was it what you were expecting?

1. Go back to Terminal and quit your application’s web server by running Ctrl-C. Then, start the rails console.

2. Now try running the following code:

   Book.find(3)
   

   What did it return? It returned the book in your application’s database with id 3.

   #<Book id: 3, title: "1984", author: "George Orwell", price_cents: 0, created_at: "2016-12-26 15:51:15", updated_at: "2016-12-26 15:51:15", quantity: 200>
   

3. What do you get when you run Book.find(1) or Book.find(5)?

   You get the book with that id.

4. What happens if you do Book.find(100)?

   ActiveRecord::RecordNotFound: Couldn't find Book with 'id'=100
   

   An error! Book.find returns an error when it doesn’t find a book with the given book id.

   So we can use Book.find to get books from your application’s database with a given id. If a book doesn’t exist with that id, we get an ActiveRecord::RecordNotFound error.

5. Exit the console and restart your application’s web server.

Let’s use our new knowledge of Book.find to get and show the requested book in the BooksController show method.

1. In your text editor, open the BooksController.

2. We’ve already grabbed the requested book id and set it to @id. Let’s use that to find the requested book.

   Add the following line to the end of the show method:

   @book = Book.find(@id)
   

3. Save your changes and go to http://localhost:3000/books/1.

   Did you notice anything different? I hope not, because we didn’t update the template 😝

1. Now, open the BooksController show template (app/views/books/show.html.erb).

2. Add the following line to the end of the file

   This book is called <%= @book.title %>
   

3. Save your changes and go back to http://localhost:3000/books/1.

1. Open app/views/books/show.html.erb in your text editor and delete everything in the file.

   Yes, EVERYTHING.

   There’s nothing wrong with what we’ve done so far, but adding the definition list is easier from scratch.

2. Now, add the following code to the file:

   <dl>
     <dt>Id</dt>
     <dd><%= @book.id %></dd>
   
     <dt>Title</dt>
     <dd><%= @book.title %></dd>
   </dl>
   

   This is an HTML definition list with a couple of terms: “Id” and “Title”. The terms are defined with values for the given book.

   Save your changes and go to http://localhost:3000/books/1 to see the results.

1. Now that we have a definition list with the book's id and title, update it to include the rest of the book's information (author, price_cents, and quantity).

1. What did you come up with? Your solution should look something like this:

   <dl>
     <dt>Id</dt>
     <dd><%= @book.id %></dd>
   
     <dt>Title</dt>
     <dd><%= @book.title %></dd>
   
     <dt>Author</dt>
     <dd><%= @book.author %></dd>
   
     <dt>Price Cents</dt>
     <dd><%= @book.price_cents %></dd>
   
     <dt>Quantity</dt>
     <dd><%= @book.quantity %></dd>
   </dl>
   

2. Update your solution to match this solution.

1. Reopen app/views/books/show.html.erb and change the “Price Cents” definition from

   <dd><%= @book.price_cents %></dd>
   

   to

   <dd><%= number_to_currency(@book.price_cents) %>
   

2. Save your changes and revist http://localhost:3000/books/1.

1. Reopen app/views/books/show.html.erb and change the “Price Cents” definition from

   <dd><%= number_to_currency(@book.price_cents) %></dd>
   

   to

   <dd><%= number_to_currency(@book.price_cents / 100.0) %></dd>
   

   To convert from cents to dollars, we can simply divide by 100.

   (Actually we have to divide by 100.0 because floating point math is fun)

   Then, the converted value is used by number_to_currency.

2. You can also go ahead and change the definition term from “Price Cents” to “Price”.

3. Save your changes and try looking up a few of your books in your browser.

1. Go back to Terminal and stop your application’s web server by running Ctrl-C.

2. Now, run rails generate migration add_description_to_books.

   This creates a new timestamped migration file db/migrate/TIMESTAMP_add_description_to_books.rb.

1. Open your new migration in your text editor.

2. Inside the change method, add the following line:

   add_column :books, :description, :text
   

   With this change, we’re setting up the migration to add a column to the books table. The new column will be named description and it will store any amount of text.

3. Save your changes.

1. Now, go back to Terminal.

   Run rake db:migrate to run your new migration against your application’s database.

Let’s take a look at how this changes your bookstore.

1. In Terminal, start rails console, get your first book and assign it to a variable called my_first_book.

   my_first_book = Book.first
   

   Does the book look different?

   At the end, you should see a nil description.

   #<Book id: 1, title: "why's (poignant) Guide to Ruby", ..., description: nil>
   

   description is nil because you just added it.

2. You can give my_first_book a description by running

   my_first_book.update(description: "YOUR INSPIRING DESCRIPTION")
   

   Where YOUR INSPIRING DESCRIPTION is…YOUR INSPIRING DESCRIPTION.

   (Don’t worry about your description being inspiring 😉)

3. After you’ve added YOUR INSPIRING DESCRIPTION to my_first_book, you can run my_first_book.description to see the new description.

4. Go ahead and add descriptions for the of rest your books. Your application’s database should have seven books, which means you have six descriptions to write.

5. When you’re done, exit the rails console and restart your application’s web server by running rails server.

1. Now that your books have descriptions, you can share them with the WORLD!

   Reopen app/views/books/show.html.erb and add the book’s description to the end of the definition list.

1. What did you come up with? You should’ve added the following lines:

   <dt>Description</dt>
   <dd><%= @book.description %></dd>
   

2. Save your changes and view your beautiful descriptions in your browser.

In HTML, you add links using anchor elements (<a> tags). Anchor elements link to other pages by their href attribute.

Fortunately, Rails gives us a convience method to abstract away some of that work.

1. In your text editor, open app/views/books/index.html.erb.

2. Change the list item that renders book titles and authors to this:

   <li>
     <%= link_to(book.title, book_path(book)) %> by <%= book.author %>
   </li>
   

   Rails gives us a link_to method we can use to create anchor elements.

   First, you give it the text for the link. In this case, we want to use the book’s title as the link text.

   Then, you give it the path for the link. We want the link to go to /books/:id, but we passed it book_path(book). book_path(book) is another Rails method. Long story short, it generates /books/:id for the given book.

3. Save your changes and go to http://localhost:3000/books. Try clicking all the links!

   When you’re done, stop your application’s web server.