Explore creating robust HTTP services in Scala's functional programming paradigm. Gain insights into pure vs. impure implementations, their pros and cons, and effective tool usage.

scala-platform.tar.gz

Scala-Pure

Scala-Impure

Scala-Tapir

Scala-Impure-Test

Scala-Pure-Test

Scala-Tapir-Test

Test

Scala - Run Code Widget 

Scala-Pure-copy

Scala is one of the most popular general-purpose languages that supports both object-oriented and functional programming. In this course, you will learn how to create back-end HTTP services using Scala's functional programming paradigm.

You will also learn how to develop, test, and document the service using both pure and impure ways. You will be exposed to the differences between pure and impure implementation, their respective pros and cons, and how pure implementation can be more robust in terms of performance, understandability, testability, and type safeness. 

By the end of the course, you will have a clear idea of how functional programming works in Scala and how you can use the available tools more effectively.

Pure Functional HTTP APIs in Scala

# Main application

Within our main entry point, we initialize all needed components and wire them together. We’ll step through each part in this section. 

The first thing you’ll notice is that we use the `IOApp` provided by the *_Cats effect_* library. 


object Pure extends IOApp {
  @SuppressWarnings(Array("org.wartremover.warts.Any"))
  def run(args: List[String]): IO[ExitCode] = ???
}

We need to suppress a warning from *wartremover* (**Line 2**) here as well. 


# Database initialization 

Let’s continue to initialize the database connection. 



val migrator: DatabaseMigrator[IO] = new FlywayDatabaseMigrator

val program = for {
  (apiConfig, dbConfig) <- IO {
    val cfg = ConfigFactory.load
    (loadConfigOrThrow[ApiConfig](cfg, "api"),
    loadConfigOrThrow[DatabaseConfig](cfg, "database"))
}
ms <- migrator.migrate(dbConfig.url, dbConfig.user, dbConfig.pass)
tx = Transactor
  .fromDriverManager[IO](dbConfig.driver,
    dbConfig.url,
    dbConfig.user,
    dbConfig.pass)
repo = new DoobieRepository(tx) 

We create our database migrator explicitly wired to the `IO` data type. 

Now, we start with a `for` comprehension in which we load our configuration via *pureconfig* yet again within an `IO`. After successfully loading the configuration, we continue with migrating the database. Review **lines 3–8**.

Finally, we create the transactor needed by *Doobie* and the database repository (**Line 15**). 

# Routes and http4s server 



Learn how to define the main entrypoint and interact with the pure implementation of the service.

Introduction

Impure Implementation

Pure Implementation

Testing Impure Services

Testing Pure Services

Benchmarks

Documentation

Epilogue

Starting the Application

Main application

Database initialization