VladimirLogachev / library

GraphQL API and frontend for offline library. Haskell, Elm, Postgres

Library

GraphQL API and frontend for the next implementation of my offline library, implemented with Haskell and Elm, using mu-haskell, postgres-typed and elm-graphql. (there is also previous implementation in Elm without backend)

Key feature: compile-time typecheck against PostgreSQL and GraphQL schemas and (both backend and frontend).

• TODO
• GraphQL queries (curl)
• URL structure
• UI design (Figma, work in progress)

Setting up and running

1. docker-compose up -d — run PostgreSQL
2. cd backend
   • stack build --exec backend --file-watch — check schemas, run API server and watch for file changes
3. cd frontend
   • npm i — install dependencies
   • npm start — generate query library from schema, start dev-server, open http://localhost:8000/:

Notes

1. stack build --ghc-options -O2 --copy-bins && ~/.local/bin/backend — API production build (later use in dockerfile)

Design choices and tradeoffs

1. Mu-haskell does not join sql queries, so I decided to exclude books from Authors. By making this tradeoff I can manually join sql queries.
2. GraphQL currently does not support input unions. But I want admin app to create book either with new author, or with existing one. What could I do:
   • Accept nullable fields in inputs: newAuthor, existingAuthorId, and then choose first filled (aka workaround input unions)
   • Decide on frontend and compose tasks that create author before book, if necessary (but it is not transactional which could be very confusing in case of any failure and retry)
   • Provide different mutations for such cases, and let frontend decide. This means enough typesafety, ability to make a proper SQL transaction and little work on frontend. This is my choice.