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HW 4: Your first Rails app (Hartl, Chapter 2)

I expect that this assignment should take you about two hours.

Warning! This assignment relies on Cloud 9. Cloud 9 is in transition. Please use the traditional Cloud 9, if possible. I’ve included notes below to explain of the primary differences.

A note from Sam

When using git, please don’t use git commit -a or git add .. You should pay attention to the individual files you’re working with. It takes only a little while longer, it’s better practice, and, in the long term, it saves you from big mistakes. (If you don’t know the alternative to git commit -a, let me know.)

Your primary task

Do all of the steps and exercises in Chapter 2 of Michael Hartl’s The Rails Tutorial. You will then answer some questions on those steps. You may find it useful to read the questions in advance.

What to submit

Send me answers to the following questions in a message entitled “CSC 321.01 2018S, HW 4: Your first Rails app (Hartl, Chapter 2) (Name)”. Please replace Name with your name.

  1. What is the URL of your Cloud 9 instance? (E.g.,

  2. As you likely noted, rails generate scaffold creates a lot of files. Explain the (likely) purpose of each of the following.

    a. db/migrate/20180111111111_create_users.rb (you will have a slightly different name)

    b. app/models/user.rb

    c. test/models/user_test.rb

    d. app/controllers/users_controller.rb

    e. app/views/users/index.html.erb

    f. test/controllers/users_controller_test.rb

  3. What files did rails generate scaffold modify? What changes did it make to those files?

  4. What changes would you have to make to the application to show the user id on the /users page?

  5. Rails often relies on “convention over configuration”. There’s a subtle instance of that principle in section 2.3.3. What unstated information is implicit in the design of the relationship between users and microposts?

  6. As Hartl notes, the toy application is not nearly robust enough. Consider, for example, the association of posts with users. As you may have noted, once we have the validation in place, Rails stops you from adding a post with an invalid user id. However, it is possible to end up with a post whose user_id does not reference a valid user. How?

  7. Hartl does not have us commit changes until we are ready to deploy to Heroku. What are some earlier steps in which a commit might be appropriate?

  8. A student who was experimenting with this application added the following line to app/views/microposts/index.html.erb. Explain what this code does.

    <td><%= micropost.user ? : "???" %></td>

Some notes on using the “traditional”

  1. Don’t forget that your work is in the workspace directory rather than the examples directory!

  2. Don’t forget to start your Rails server with

    rails server -b $IP -p $PORT

  3. In section 2.3.4, Hartl references ApplicationController. You may find that your application is using ApplicationRecord instead.