Simple full stack web app for tracking workouts.
A live demo of the app is hosted here. It is "secured" with the basic auth credentials "demo" "demo". The data entered there is reset on a daily basis. The demo might be taken offline at any point in the future without updating the readme. The main pages (landing page and workout page) look like this:
- We can use smart constructors to enforce validation logic when trying to create a type. See usage of mkExercise for an example of this.
- We can encode knowledge in types (e.g. NonEmpty [a]) in order to avoid doing the same check (list is not empty).
- We can short circuit execution by matching on a constructor (e.g. see DB.hs
Right exercises <- getExercisesForWorkout conn $ exerciseWorkoutId x). If the result is not a Right x the code short circuits by returning the resulting Left. - Error/Exception handling. After asking why postgresql-simple does throw exceptions instead of use Either for modelling them, I got told that most Haskell libraries make tradeoffs in beginner friendlyness (in the form of low/no stacking of monads) and error/exception handling. For example the query function in postgresql-simple which is used to query the database returns IO [r] where r is assumed to be the data type you are handling with a FromJson and ToJson instance. E.g. Exercise or Workout for this app. See query documentation here. I would expect/prefer a return type of IO (Either Text r) which means that we have error/exception handling baked in and not as an afterthought. I don't know how common this is, but this is what I adapted the DB module to and currently prefer. I got around this by creating a custom exception handler and wrapping the database calls with this wrapper. E.g. see 'unsafeDeleteWorkoutWithExercises' and 'deleteWorkoutWithExercises'.
- Ensure you have ghc and cabal installed. I used ghcup to get these and used ghc 9.2.7 and cabal version 3.6.2.0.
- dbmate installed for raw SQL migrations
- docker and docker-compose installed
- libpq-dev installed (for ubuntu 20.04 run
apt install libpq-dev) I think this was required to be able to build postgresql-simple..?
- Set up environment variables
cp env.local .env - Start postgresql/database
docker-compose up -d - Create the database
dbmate create - Create the tables for our app
dbmate up - Install dependencies and build the app
cabal build - Run the app
cabal run app - Browse http://localhost:3000 to use the app
- For development it might be useful to run
bash watch-and-rebuild.shif you have inotify-watch installed it will then automatically rebuild whenever you make and save changes to the app.
- dbmate is used for migrations, check their docu there if in doubt.
- Run dbmate to create migrations. Use snake_case since this is the default for
postgres and dbmate. E.g.
dbmate new add_origin_created_at_to_recipes - A file will created which looks like this
-- migrate:up
-- migrate:down
I would suggest to host this app behind basic auth with secure credentials. For the deployment, my automated deployment setup for GitLab can be found under ./.gitlab-ci.yml. I simply have a nginx reverse proxy in front of the app secured with basic auth.
Happy about suggestions and improvements to the small code base. If you find something confusing about "todo-app" in this code it is because I started with the previous small project haskell-simple-todo as baseline and did not bother to adapt it in all places.