http4s-newtype-refined-doobie-crud

What is it?

A pet project where I experiment/learn various libraries/technics/patterns.

Tech Stack

• Http4s
• Doobie
• Circe
• Cats
• Refined
• NewType
• Tapir
• OpenTracing
• Enumeratum
• PureConfig
• Quill
• ScalaTest

Domain

Car adverts should have the following fields:

• id (required): int or guid, choose whatever is more convenient for you;
• title (required): string, e.g. "Audi A4 Avant";
• fuel (required): gasoline or diesel, use some type which could be extended in the future by adding additional fuel types;
• price (required): integer;
• new (required): boolean, indicates if car is new or used;
• mileage (only for used cars): integer;
• first registration (only for used cars): date without time.

Functionality:

• have functionality to return list of all car adverts;
• optional sorting by any field specified by query parameter, default sorting - by id;
• have functionality to return data for single car advert by id;
• have functionality to add car advert;
• have functionality to modify car advert by id;
• have functionality to delete car advert by id;
• have validation (see required fields and fields only for used cars);
• accept and return data in JSON format, use standard JSON date format for the first registration field.

Code

Domain models

Case classes designed using NewType and Refined. I believe this approach provides the best experience when it comes to dealing with invalid data.

API design:

I used Tapir to describe endpoints. I liked the idea of describing endpoints in type safe manner. At the beginning, there was a learning curve, but I really liked the final result.

Tagless Final:

I was not really experience in that regard, but I wanted to use Tagless Final just to see how it feels. However, I think it was a bit overkill for this sample project.

Validation:

I used cats.Validated for validating user inputs and business logics. It's very easy to use, and at the end we get accumulated errors.

Compiler Plugins:

I am using 4 compiler plugin in this project to enable some fancy(missing) features of scala compiler. I would suggest you to read github page of each plugin to at least understand why it exists. I think almost all of them won't be needed anymore once we have Scala 3