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part_3_connecting_hangperson_to_sinatra.md

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Part 3: Connecting HangpersonGame to Sinatra

You've already met Sinatra. Here's what's new in the Sinatra app skeleton app.rb that we provide for Hangperson:

  • before do...end is a block of code executed before every SaaS request

  • after do...end is executed after every SaaS request

  • The calls erb :action cause Sinatra to look for the file views/action.erb and run them through the Embedded Ruby processor, which looks for constructions <%= like this %>, executes the Ruby code inside, and substitutes the result. The code is executed in the same context as the call to erb, so the code can "see" any instance variables set up in the get or post blocks.

Self Check Question

`@game` in this context is an instance variable of what class? (Careful-- tricky!)

It's an instance variable of the `HangpersonApp` class in the app.rb file. Remember we are dealing with two Ruby classes here: the `HangpersonGame` class encapsulates the game logic itself (that is, the Model in model-view-controller), whereas `HangpersonApp` encapsulates the logic that lets us deliver the game as SaaS (you can roughly think of it as the Controller logic plus the ability to render the views via `erb`).

The Session

We've already identified the items necessary to maintain game state, and encapsulated them in the game class. Since HTTP is stateless, when a new HTTP request comes in, there is no notion of the "current game". What we need to do, therefore, is save the game object in some way between requests.

If the game object were large, we'd probably store it in a database on the server, and place an identifier to the correct database record into the cookie. (In fact, as we'll see, this is exactly what Rails apps do.) But since our game state is small, we can just put the whole thing in the cookie. Sinatra's session library lets us do this: in the context of the Sinatra app, anything we place into the special "magic" hash session[] is preserved across requests. In fact, objects placed there are serialized into a text-friendly form that is preserved for us. This behavior is switched on by the Sinatra call enable :sessions in app.rb.

There is one other session-like object we will use. In some cases above, one action will perform some state change and then redirect to another action, such as when the Guess action (triggered by POST /guess) redirects to the Show action (GET /show) to redisplay the game state after each guess. But what if the Guess action wants to display a message to the player, such as to inform them that they have erroneously repeated a guess? The problem is that since every request is stateless, we need to get that message "across" the redirect, just as we need to preserve game state "across" HTTP requests.

To do this, we use the sinatra-flash gem, which you can see in the Gemfile. flash[] is a hash for remembering short messages that persist until the very next request (usually a redirect), and are then erased.

Self Check Question

Why does this save work compared to just storing those messages in the `session[]` hash?

When we put something in `session[]` it stays there until we delete it. The common case for a message that must survive a redirect is that it should only be shown once; `flash[]` includes the extra functionality of erasing the messages after the next request.

Running the Sinatra app

As before, run the shell command rackup -p $PORT -o $IP to start the app, or rerun -- rackup -p $PORT -o $IP if you want to rerun the app each time you make a code change.

Self Check Question

Based on the output from running this command, what is the full URL you need to visit in order to visit the New Game page?

The web server connected to Sinatra is running on Cloud9, so the first part of the URL is something like `http://your-workspace-name.c9.io`. The Ruby code `get '/new' do...` in `app.rb` renders the New Game page, so the full URL is in the form `http://your-workspace-name.c9.io/new`.

Visit this URL and verify that the Start New Game page appears.

Self Check Question

Where is the HTML code for this page?

It's in `views/new.erb`, which is processed into HTML by the `erb :new` directive.

Verify that when you click the New Game button, you get an error. This is because we've deliberately left the <form> that encloses this button incomplete: we haven't specified where the form should post to. We'll do that next, but we'll do it in a test-driven way.

Let's get our app onto Heroku.

  • First, run bundle install to make sure our Gemfile and Gemfile.lock are in sync.
  • Next, type git add -A to stage all changed files (including Gemfile.lock)
  • Then type git commit -am"Ready for Heroku!" to commit all local changes on Cloud9.
  • Next, type heroku login and authenticate.
  • Since this is the first time we're telling Heroku about the Hangperson app, we must type heroku create to have Heroku prepare to recieve this code and to have it create a git reference for referencing the new remote repository.
  • Then, type git push heroku master to push your Cloud9 code to Heroku.
  • When you want to update Heroku later, you only need to commit your changes to git locally in Cloud9, then push to Heroku as in the last step.
  • Verify that the Heroku-deployed Hangperson behaves the same as your development version before continuing. A few lines up from the bottom of the Heroku output in the Cloud9 terminal should have a URL ending in herokuapp.com. Find that, copy it to the clipboard, and paste it into a new browser tab to see the current app. The Cloud9 IDE browser tab won't render the app properly, so use a new browser tab outside of Cloud9.
  • Verify the broken functionality by clicking the new game button.

Next: Part 4 - Cucumber