CHIPS 4.8: Hello Rails
Create your first Rails app from scratch — RottenPotatoes, the movie-ratings app you’ll grow throughout the rest of the course — and deploy it to the cloud. This is part of Module 4.
The full, step-by-step assignment lives in the starter repo,
saasbook/hw-hello-rails:
start with its README.md
and work through it in order.
CHIPS 4.8 is a group assignment — work on it and submit it with your team of 4.
Goals
- Create a new Rails app and get it running locally: dependencies, database setup, migrations, and seed data.
- Trace the MVC flow end-to-end: route → controller action → model → view.
- Implement the basic CRUD actions (create, read, update, delete) for a resource.
- Deploy a Rails app to the cloud.
- Debug when things go wrong, using logs and the techniques from §4.7.
What you’ll do
You’ll build RottenPotatoes, an app for cataloging movies: users can create new movie entries, view and edit a movie’s details (title, rating, description, and so on), and delete movies. We provide some starter code you can copy and paste into specific files, but you will do most of the work. Once the app runs locally, you’ll deploy it on the public cloud.
Before you start
Finish the Module 4 videos and readings.
Logistics
- Getting the code: see Getting the Code below — you clone the public starter repo and push it to a private repo of your own.
- Autograding: submit to Gradescope; you may submit as many times as you like before the deadline. The autograder is a way for you to check your work and your understanding. Run the tests locally first — see Running Code and Tests.
- Deployment: put the URL of your deployed app in
rottenpotatoes-url.txtbefore you submit. - Extensions: everyone automatically gets a 2-day no-penalty extension; see the extension policy.
- Collaboration: you may collaborate with your team of 4, and discuss high-level approaches with anyone. Sharing code outside your team is academic misconduct. See the AI Use Policy below before using AI tools.
AI Use Policy
This assignment follows the course AI Policy, which will be published on this site before it is needed. Until then, the rule from the Syllabus applies: you must be able to explain everything you submit.
Getting the Code
Public starter repo: saasbook/hw-hello-rails —
https://github.com/saasbook/hw-hello-rails
GitHub makes it challenging to have a private fork of a public repository. These steps allow you to create a private space for you own work but still update from the starter code.
Clone the starter repo, then use gh
(see Local Development)
to create a private copy under your own GitHub account and
push the code to it. Replace YOUR_GITHUB_USERNAME with your
GitHub username:
git clone https://github.com/saasbook/hw-hello-rails.git
cd hw-hello-rails
git remote rename origin upstream
gh repo create YOUR_GITHUB_USERNAME/hw-hello-rails --private --source=. --remote=origin --push
git remote set-url --push upstream DISABLED
After this, origin is your private repo and upstream
is the public starter repo. The last command disables pushing to
upstream, so git push always goes to your own
copy — never to the public starter repo.
Keeping your repo up to date
Your private repo is a snapshot: it does not follow the starter
repo. If we fix or add something in saasbook/hw-hello-rails
after you copy it, you have to pull those changes in yourself. The
upstream remote you set up above is how you do that:
git fetch upstream
git fetch only downloads — it changes nothing in your working
copy. Review what you are about to take before merging it:
git diff --name-only HEAD upstream/main # just the names of the files that differ
git diff --stat HEAD upstream/main # the same list, plus how much changed in each
git diff HEAD upstream/main -- spec # the actual changes, limited to one file or directoryThen merge the upstream changes into your branch and push them to your private repo:
git merge upstream/main
git push origin main
If you and we edited the same lines, git stops and reports a conflict: open
each file it lists, keep the correct combination of both sides, delete the
<<<<<<< / ======= /
>>>>>>> markers, then git add
those files and git commit. Ask on Ed if a merge leaves you
stuck — don't start over and lose your work.
These commands assume the starter repo's default branch is main.
If git branch -r shows upstream/master instead, use
that name in the commands above.
View this assignment on bCourses.
Running Code and Tests
Run everything below from the root of your clone (see Getting the Code). If Ruby isn't installed yet, work through Local Development first.
Install the dependencies
bundle install
Run this once after cloning, and again whenever the Gemfile
changes. Prefix the commands below with bundle exec so you run
the same gem versions the autograder does.
Boot the project
Create the database (once, and after any new migration), then start the Rails server:
bin/rails db:migrate
bin/rails serverThe app is then at http://localhost:3000; Control-C stops the server. To try one thing without clicking through the UI, use the console, which loads your app and its models:
bin/rails consoleRun the tests
Run the RSpec suite the way the Gradescope autograder will — get it green locally before you submit:
bundle exec rspec # the whole suite
bundle exec rspec spec/YOUR_FILE_spec.rb # one spec file
bundle exec rspec spec/YOUR_FILE_spec.rb:42 # one example, by line number
bundle exec rspec --format documentation # every example's descriptionEach failure prints the file and line of the failing example along with what it expected — start there rather than at the top of the output.