Ruby on Rails to Kotlin

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How to convert from Ruby on Rails to Kotlin

Converting a project from Ruby on Rails to Kotlin can be an elaborate process, requiring attentiveness to detail and a well-thought-out plan. In this guide, we will dive deep into the steps and considerations necessary for a smooth transition.

Understanding the Differences Between Ruby on Rails and Kotlin

Before beginning the conversion, it's essential to understand the fundamental differences between Ruby on Rails and Kotlin.

Ruby on Rails is a server-side web application framework written in Ruby. It follows the convention over configuration (CoC) and don't repeat yourself (DRY) principles.

Kotlin, on the other hand, is a statically typed programming language that runs on the Java Virtual Machine (JVM). Although different from Ruby, Kotlin is versatile and can be used to build web applications when paired with frameworks like Ktor.

Preparing for the Conversion

Assessing Your Ruby on Rails Application

Start by conducting a thorough assessment of your current Ruby on Rails application. Document all key components, including models, controllers, views, services, and background jobs. Understanding the structure and dependencies of your existing application will help in planning the conversion process.

Setting Up Your Kotlin Environment

Ensure you have Kotlin and the necessary development tools installed. Setting up JetBrains IntelliJ IDEA with Kotlin support will streamline your development process. If you choose to use Ktor as your Kotlin web framework, be sure to install it and go through its basic documentation.

Converting Models

In Ruby on Rails, models are typically created using Active Record, an Object-Relational Mapping (ORM) framework. Converting these models to Kotlin will require a similar ORM or creating plain Kotlin classes that interact with your database.

Ruby on Rails Model Example

class User < ApplicationRecord
  has_many :posts
  validates :email, presence: true

Equivalent Kotlin Model

Using an ORM like Exposed, a Kotlin model may look like this:


object Users : Table() {
    val id = integer("id").autoIncrement().primaryKey()
    val email = varchar("email", 255).uniqueIndex()

class User(id: EntityID<Int>) : IntEntity(id) {
    companion object : IntEntityClass<User>(Users)
    var email by
    // Define relationships with other tables

Converting Controllers

Ruby on Rails follows the MVC (Model-View-Controller) pattern, where controllers are responsible for handling HTTP requests and responses. In Kotlin with Ktor, you would create routing handlers to manage these requests.

Ruby on Rails Controller Example

class UsersController < ApplicationController
  def index
    @users = User.all

Equivalent Kotlin Handler

Using Ktor, your handler may look like this:

import io.ktor.application.*
import io.ktor.response.*
import io.ktor.routing.*

fun Route.userRoutes() {
    route("/users") {
        get {
            // Fetch and serialize users here
            call.respond(//... list of users)

Converting Views

Rails uses ERB (Embedded Ruby) for templating views. When moving to Kotlin, you can use Ktor's built-in templating or choose other templating libraries like Thymeleaf or FreeMarker.

Ruby on Rails View Example (ERB)

<% @users.each do |user| %>
  <p>Email: <%= %></p>
<% end %>

Equivalent Kotlin View

Using Ktor with FreeMarker:

<#list users as user>
    <p>Email: ${}</p>

Converting Routes

In Rails, routes are defined in the config/routes.rb file. With Ktor, you'd configure routing using DSL (Domain Specific Language).

Ruby on Rails Routes

Rails.application.routes.draw do
  resources :users, only: [:index, :show]

Equivalent Ktor Routing

fun Application.module() {
    routing {
        userRoutes() // previously defined route handlers

Handling Dependencies

Ruby on Rails uses Bundler to manage gems, while Kotlin uses Gradle or Maven to manage dependencies.

Gemfile Example

gem 'rails', '~> 6.0'
gem 'pg', '>= 0.18', '< 2.0'

Equivalent Gradle Dependencies

dependencies {

Testing Your Kotlin Application

Just as in Rails, testing is paramount. Rails uses RSpec or Minitest for testing, whereas Kotlin can use JUnit or TestNG.

Ruby on Rails Test Example

RSpec.describe User, type: :model do
  it "is valid with valid attributes" do
    user = "")
    expect(user).to be_valid

Equivalent Kotlin Test

Using JUnit:

import org.junit.jupiter.api.Assertions.*
import org.junit.jupiter.api.Test

class UserTest {
    fun `test user creation with valid email`() {
        val user = User(email = "")

Final Thoughts on Your Free Ruby on Rails to Kotlin Code Converter

While the conversion process may seem daunting, understanding the distinctions and similarities between the frameworks can simplify your journey. Be mindful of testing at each stage to ensure the functionality remains intact. By breaking down the migration into manageable steps, you can ensure a seamless transition from Ruby on Rails to Kotlin.

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