Build Drag and Drop with Rails Hotwire

Introduction

Hey there, fellow web adventurers! 😄 Building web applications can be a wild ride, right? Well, today, we're diving into something super cool: adding drag-and-drop functionality to your Rails app, all powered by the magic of Hotwire! No worries, we won't start from scratch – we're keeping it hush-hush and diving straight into the fun part. 💫

Shhh... Our Little Secret Tool

We've got a secret weapon up our sleeves: UpperBracket. It's like having a magic wand for generating full-stack Rails applications. It comes with all the goodies – Vite, Tailwind CSS, Rodauth, Rubocop, and more – so we can focus on the fun stuff. Let's keep this between us, though! 😉

Curious about the final result, here it is

Let’s build

So, what's the plan? We're creating a simple course list app where users can rearrange items with a flick of their mouse. Super cool, right? Let's kick things off by generating our Rails app using the UpperBracket template.

# create app
rails new hotwire-dragndrop \
  -d postgresql \
  -m https://raw.githubusercontent.com/maful/upperbracket/main/template.rb

# move to the app directory
cd hotwire-dragndrop

• Make sure you've got your PostgreSQL database up and running before we dive in.

Create Course model with only title attribute, no fancy here.

rails g scaffold Course title

Open the generated migration for the courses table and define that title should not be null.

class CreateCourses < ActiveRecord::Migration[7.0]
  def change
    create_table :courses do |t|
      t.string :title, null: false

      t.timestamps
    end
  end
end

Add presence validation for the title in the Course model app/models/course.rb

# frozen_string_literal: true

class Course < ApplicationRecord
  validates :title, presence: true
end

Update the routes to set the root page to the courses list page config/routes.rb

# frozen_string_literal: true

Rails.application.routes.draw do
  root "courses#index"
  resources :courses
end

I’m going to add a small styling for the page with Tailwind CSS, this is optional. Open the course index page app/views/courses/index.html.erb and update with the following code

<div class="container">
  <div class="max-w-screen-md mx-auto py-10">
    <p style="color: green"><%= notice %></p>

    <div class="mb-6">
      <%= link_to "New course", new_course_path, class: "rounded border border-slate-500 px-2 py-3" %>
    </div>

    <h1 class="text-2xl font-medium mb-4">Courses</h1>

    <div id="courses" class="flex flex-col gap-4">
      <%= render @courses %>
    </div>
  </div>
</div>

Open the single course page in app/views/courses/_course.html.erb

<div
  id="<%= dom_id course %>"
  class="bg-gray-50 shadow-sm space-y-6 py-6 px-4"
>
  <div class="flex gap-4 items-center">
    <div class="text-gray-700 text-base">
      <%= course.title %>
    </div>
  </div>
</div>

Run rails db:migrate to run the database migration. You can now run the application using bin/dev

Add some courses to the application and you should now have something like this

You have a list of courses now and quite looks good for simple application. However, this isn’t the end and notice that we are still unable to drag and drop the course.

Adding Sortable Library

It is time to adding the main functionality drag and drop, add ranked-model gem to handle record ordering in the backend

bundle add ranked-model

And add node packages for reorderable library and http request

yarn add sortablejs @rails/request.js

Create migration to add row_order column to courses table

rails generate migration AddRowOrderToCourses row_order:integer

row_order column is nullable, and we already added some courses in the previous section. Let’s fill the row_order for the existing records in the courses table.

rails generate migration BackfillRowOrderToCourses

Update the generated migration file with this code

class BackfillRowOrderToCourses < ActiveRecord::Migration[7.0]
  disable_ddl_transaction!

  def up
    Course.unscoped.in_batches do |relation|
      relation.update_all('row_order = EXTRACT(EPOCH FROM created_at)')
      sleep(0.01)
    end
  end
end

This migration basically disable DDL (Data Definition Language) during migration of this file, then iterate over course records in batches and update the row_order from the created_at data. Execute the new migration by running rails db:migrate

Open the Course model and include the ranked-model gem and configure it.

# frozen_string_literal: true

class Course < ApplicationRecord
  include RankedModel

  ranks :row_order
end

Now, open the app/controllers/courses_controller.rb and update the @courses variable in index method to use ranked-model for the ordering

def index
-  @courses = Course.all
+  @courses = Course.rank(:row_order).all
end

Run the application and and check the courses page. Nothing difference in the context of UI, but if you check the development log, you will notice that the row_order has been use for for ordering record.

Course Load (1ms)  SELECT "courses".* FROM "courses" ORDER BY "courses"."row_order" ASC

Create Sortable Stimulus Controller

In previous section, we have install sortable node package, in this section we’re going to use it. Create stimulus controller named sortable in app/javascript/controllers/sortable_controller.js and add the following code

import { Controller } from "@hotwired/stimulus"
import Sortable from "sortablejs"

export default class extends Controller {
  connect() {
    const options = {
      onEnd: this.onEnd.bind(this)
    }
    Sortable.create(this.element, options)
  }

  onEnd(evt) {
    const body = { row_order_position: evt.newIndex }
    console.log(body)
  }
}

Explanation

• Import the sortablejs to the controller
• Override the connect function to create the Sortable instance for the current element. Meaning that it will register the element where you connect with the sortable controller.
• Imagine you've just dragged an item to its new spot. What's next? We're adding a function called onEnd. It's like the grand finale of a show! But here's the twist – we're not sending data to the backend just yet. Instead, we're logging the new index to keep an eye on the changes.

Let’s try to connect the stimulus controller to our element. Open app/views/courses/index.html.erb file and add data-controller="sortable" to the div element with id courses

<div id="courses" class="flex flex-col gap-4" data-controller="sortable">

Now, let's put our work to the test! Fire up your app and give that course list a spin. You'll notice that you can drag and drop items, and the item you drag will change its position. Check your browser console to see the new position in action!

But here's the catch – when you refresh the app, it's like hitting the rewind button. Why? Because we haven't saved the changes to the database yet.

The position is based on the index, and index in JavaScript is start from 0. If you check again in sortable_controller.js, the body variable is what we need to send to the backend and backend save it to the database. Let’s do it, in the onEnd function, remove the console.log line because we don’t need it anymore. So here is the final sortable_controller.js for now.

The position we're talking about is based on the index. Quick heads-up – in JavaScript, the index starts at 0. Peek at sortable_controller.js, and you'll find the body variable. That's the golden nugget we need to send to the backend for database saving.

In the onEnd function, we're saying goodbye to the console.log line – we don't need it anymore. Here's our polished sortable_controller.js for now.

import { Controller } from "@hotwired/stimulus"
import Sortable from "sortablejs"
import { patch } from "@rails/request.js"

export default class extends Controller {
  connect() {
    const options = {
      onEnd: this.onEnd.bind(this)
    }
    Sortable.create(this.element, options)
  }

  onEnd(evt) {
    const body = { row_order_position: evt.newIndex }
    patch(evt.item.dataset.sortableUrl, {
      body: JSON.stringify(body),
      responseKind: "turbo-stream",
    })
  }
}

Oh, and one last thing – you'll spot evt.item.dataset.sortableUrl in the code. It's like a map to where the request should be sent. Let's create a route for it by opening up the routes and adding the rank with the patch method to the courses resources.

resources :courses do
  patch "rank", on: :member
end

Open the courses_controller.rb and add new method called rank, this will update the row_order in the course record

def rank
  @course.update(row_order_position: params[:row_order_position])
end

Don’t forget to include the rank method in the before_action callback at the top

- before_action :set_course, only: [:show, :edit, :update, :destroy]
+ before_action :set_course, only: [:show, :edit, :update, :destroy, :rank]

Open app/views/courses/_course.html.erb and add data-sortable-url attribute which contains the route that we created just now

<div
  id="<%= dom_id course %>"
  class="bg-gray-50 shadow-sm space-y-6 py-6 px-4"
  data-sortable-url="<%= rank_course_path(course) %>"
>

If you inspect the element, you should see something like this

So, the code evt.item.dataset.sortableUrl is to find the value of data-sortable-url on the item being dragged.

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Let’s try again the application, the order of the position should be persisted in the database now.

Bonus 1

So, you've nailed the drag-and-drop with Hotwire in Rails, but here's a cool UX upgrade we can sprinkle in. How about adding a little marker to highlight where your item will land in the list? Let me show you what I mean. Open up your trusty sortable_controller.js and introduce the ghostClass option within the connect function.

const options = {
  onEnd: this.onEnd.bind(this),
  ghostClass: "bg-red-300"
}

If you try the app again, you'll see a red background at the new position of the dragged item.

Bonus 2

But wait, there's more! Here's another tip for you – what if you want to be super specific about which elements can be dragged and which ones stay put? Well, it's all about using the handle selector. Each element will look a little something like this:

First, add move icon in the left side of the course title. Here is the complete of app/views/courses/_course.html.erb file

<div
  id="<%= dom_id course %>"
  class="bg-gray-50 shadow-sm space-y-6 py-6 px-4"
  data-sortable-url="<%= rank_course_path(course) %>"
>
  <div class="flex gap-4 items-center">
    <div class="sortable-handle cursor-grab">
      <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-move h-4 w-4 text-current"><path d="m5 9-3 3 3 3M9 5l3-3 3 3M15 19l-3 3-3-3M19 9l3 3-3 3M2 12h20M12 2v20"/></svg>
    </div>
    <div class="text-gray-700 text-base">
      <%= course.title %>
    </div>
  </div>
</div>

Open app/views/courses/index.html.erb and add data-sortable-handle-selector-value attribute after the data-controller

<div id="courses" class="flex flex-col gap-4" data-controller="sortable" data-sortable-handle-selector-value=".sortable-handle">

And also add handle selector in sortable_controller.js and define the Stimulus values to store the value of data-sortable-handle-selector-value attribute.

import { Controller } from "@hotwired/stimulus"
import Sortable from "sortablejs"
import { patch } from "@rails/request.js"

export default class extends Controller {
  static values = {
    handleSelector: String,
  }

  connect() {
    const options = {
      onEnd: this.onEnd.bind(this),
      ghostClass: "bg-red-300"
    }
    if (this.hasHandleSelectorValue) {
      options.handle = this.handleSelectorValue
    }
    Sortable.create(this.element, options)
  }

  onEnd(evt) {
    const body = { row_order_position: evt.newIndex }
    patch(evt.item.dataset.sortableUrl, {
      body: JSON.stringify(body),
      responseKind: "turbo-stream",
    })
  }
}

Let’s check again the final result of our application

Notice the difference here, only elements with class sortable-handle that can be dragged, the rest of the element back to the normal element.

Conclusion

With Stimulus, you've got a powerful tool to take your app's interactivity up a notch. For even more awesome features and Stimulus wizardry, check out the Stimulus Documentation.

And that's a wrap, folks! 🎉 We've successfully built a slick list that you can drag and drop like a pro, and guess what? It's all snugly persisted in the database. But hey, don't stop here – you can take it further by adding topics to each course and letting users drag and drop topics across different courses. Sounds intriguing, right? You can make it happen using the group options in Sortablejs.

Full source code can be download on hotwire-sortable repository.

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