Clean Arch Example

An implementation of Clean Architecture in Scala. We will implement a simple blog application using Clean Architecture in Scala. The bellow image is a schematic of our clean architecture style.

Subprojects:

I will walk through the following projects to show the process of creating a Scala Application using Clean Architecture and some frameworks:

1. Clean Architecture
   1. Template
   2. Domain
   3. Contract
   4. Application
2. Improvements
   1. Handling Exceptions
   2. Future Utils
   3. Update with Action
3. Test
   1. Test
4. Dependency Injection
   1. Dependency Injection with Guice
5. REST Server
   1. REST Server with Play
   2. REST Server with Finatra
   3. REST Server with Akka
6. Connect to Databases
   1. Connect to Databases using Slick
   2. Connect to Databases using ScalikeJDBC

1. Clean Architecture

1. Template

Directories and abstraction of contract.service.Service.

For more information about this section visit my blog - Clean Architecture in Scala.

2. Domain

Design of classes and implementation of simple class-related use cases.

For more information about this section visit my blog - Implementing a Clean Architecture Application in Scala - Part 1 .

3. Contract

Signature of services and callbacks.

• Services should extend c.s.Service and have only one public method which is c.s.Service.call.
• Callbacks should contain only the abstraction of CRUD operations without any logic.
• Callbacks do not take execution context as a parameter and should take one from their parent module (R.T. #4 Application).

For more information about this section visit my blog - Implementing a Clean Architecture Application in Scala - Part 1 .

4. Application

Implementation of repositories, use cases, and modules.

• Repositories should implement callbacks and have only public members which their parent has.
• Use cases should implement services and should have only one public member which is c.s.Service.call.
• Use cases should use instances of callbacks (NOT repositories).
• All configurations should be placed in modules package.
• There are three essential modules
  1. Loading the config and validating it happens in modules.ConfigModule.
  2. Callbacks should be bound to repositories in modules.CallbackModule.
  3. Services should be bound to use cases in modules.ServiceModule.
• Each type of external data source and entry should have exactly one module.
  • All repositories using database should extend modules.DatabaseModule
  • All repositories using REST API and a special HTTP client should extend modules.RESTModule

Here are some tips about config files.

• An important security point is NOT to commit config files. Put some entries to ignore config files in .gitignore file.
  • application.conf
  • application.staging*.conf
  • application.prodcution*.conf
• Store all config files in one directory i.e. the project root, resources. I recommend using resources directory.
• It is essential to specify the template of config file, and I recommend committing application.template.conf with dummy values.
• There are multiple ways to specify the config file which we want to run the application with. We are using config library of com.typesafe to load configs.
  • It utilises HOCON files to load configs.
  • Expectedly, this library offers c.t.c.ConfigFactory.parseFile function to parse config file. You may set an environment variable to specify the config file and load it using this function.
  • A more elegant method is to use -DConfig.file JVM option and use this function ConfigFactory.load().withFallback(ConfigFactory.defaultApplication()).resolve.

1. Improvements

1. Handling Exceptions

Reserved

2. Future Utils

Reserved

3. Update with Action

Reserved

2. Test

1. Test with ScalaTest

RESERVED

2. Test with ScalaTest and Mockito

RESERVED

3. Dependency Injection

1. Dependency Injection with Guice

Initialized.

4. REST Server

1. REST Server with Play

RESERVED

2. REST Server with Finatra

Initialized.

3. REST Server with Akka

RESERVED

5. Connect to Databases

1. Connect to Databases with Slick

RESERVED

2. Connect to Databases with ScalikeJDBC

RESERVED

Read More

For more information about this repository, visit my blog.

Contributing

Please create an issue to suggest a new concept, framework, or library.

Implement current concepts using mentioned frameworks or libraries, and send a PR. PRs are always welcome.