gotofun

This is a sample application that demonstrates a local-first architecture for a Flutter app with a Rails backend, using PowerSync as a sync layer. Local-first means that the app works offline and syncs data when it comes back online. This is a useful pattern for mobile apps, especially when the app needs to work in areas with poor connectivity.

Local-first also has some useful ancillary benefits:

• App startup is faster because the app can display data from the local cache before any network requests are complete.
• All data is stored in a SQLite database, making local state management simpler.
• Much of the complexity of handling API interaction, including network errors and retries is handled by PowerSync.

The app displays a list of fun things to do. It also provides some example code for adding new items to the DB. Building a full mobile mobile UI for this is left as an exercise for the reader.

The backend provides some scaffolding for adding new items and a simple REST API that can be used for updates. Both of these are very lightly modified Rails scaffolding.

The backend also implements authentication endpoints as required by PowerSync (JWT generation and a JKWKS endpoint).

Setup

1. Deploy the Rails app to a server somewhere. I used Fly.io.
2. Deploy the Flutter app to a device or emulator.
3. Read the individual backend and app READMEs for detailed setup info.

Fly.io Setup

First, install the flyctl CLI

Then, create your fly app:

cd gotofun-backend
flyctl launch
# if you're on a free plan, run this with --ha=false
fly deploy

You now need to make the DB accessible to the internet, so that PowerSync can connect to it.

Fly has instructions for doing this here.

The docs are a little vague on how to get the username and password to connect to the DB. I found the easiest way was:

# if you're on a free plan, you need to run fly open first to get your app running
fly console
ENV['DATABASE_URL']

You can then extract your username and password from the URL.

In the connection string replace the Fly internal hostname with the public hostname for your DB app. This normally involves replacing the .flycast part of the hostname with .fly.dev.

Something like this:

postgres://user:password@gotofun-backend-db.flycast:5432/gotofun_backend?sslmode=disable

becomes

postgres://user:password@gotofun-backend-db.fly.dev:5432/gotofun_backend?sslmode=disable

Now you can use the connection string to connect to the DB from your local machine.

psql -Atx "postgres://..."

Follow the normal Powersync instructions to set up your DB for Powersync.