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

# Global operations

Now that our parts are in place, we can write an integration test for our repository implementation. 
First, we need to do some things globally for the test scope. 


private val dbConfig: DatabaseConfig[JdbcProfile] =
    DatabaseConfig.forConfig("database", system.settings.config)
private val repo = new Repository(dbConfig)

override protected def beforeEach(): Unit = {
    flyway.clean()
    val _ = flyway.migrate()
    super.beforeEach()
}

override protected def afterEach(): Unit = {
    flyway.clean()
    super.afterEach()
}

override protected def afterAll(): Unit = {
    repo.close()
    super.afterAll()
} 

Here, we clean our database, run the **migration**, and after we have executed all the tests, close the repository.

> Remember: not cleaning the database between tests might be an even more thorough test. 
# `loadProduct`

Let’s move on to the test for loading a single product. 


"#loadProduct" when {
    "the ID does not exist" must {
        "return an empty list of rows" in {
            val id = UUID.randomUUID
            for {
                rows <- repo.loadProduct(id)
            } yield {
                rows must be(empty)
            }
        }
    }
    
    "the ID exists" must {
        "return a list with all product rows" in {
            genProduct.sample match {
                case None => fail("Could not generate data sample!")
                case Some(p) => 
                    for {
                        _ <- repo.saveProduct(p)
                        rows <- repo.loadProduct(p.id)
                    } yield {
                        Product.fromDatabase(rows) match {
                            case None => fail("No product created from database rows!")
                            case Some(c) => 
                            c.id must be(p.id)
                            c mustEqual p
                        }
                    } 
            }
        }
    }
}


We create one Repository instance for all our tests here. The downside is that if one test crashes, the others will be affected too. On the other hand, we avoid running into database connection limits and severe code limbo to ensure closing a repository connection after each test, no matter the result. We also clean and migrate before each test and clean after each test as well.

Loading a non-existing product must not produce any result and is easy to test if our database is empty. Testing the loading of a real product is not a lot more complicated, either. We use the *ScalaCheck* generators to create one, save it, and load it again. The loaded product must, of course, be equal to the saved one. 

>You might have noticed that we do not use `forAll` here and thus are testing only one case. This is due to an issue that has yet to be fixed in *ScalaTest*. 


Learn how to perform integration testing for loading, saving, and updating a product.

Introduction

Impure Implementation

Pure Implementation

Testing Impure Services

Testing Pure Services

Benchmarks

Documentation

Epilogue

Testing the Repository

Global operations

`loadProduct`