Common Core JS Quick Setup

Common Core JS is a FANTASTIC tool to take to a hackathon. Common Core JS empowers historically underprivileged (black, brown, queer, women) developers to create tools to build the next generation of applications ourselves (not waiting on historically-privileged venture capitalists to give money, permission, and authority).

Common Core JS is also a great way to learn back-end development if you’re interested in learning Ruby on Rails. Use Common Core to build prototypes that will work with fully front-end paradigms like React, Vue, and Angular, too.

I am pleased to announce a rapid application development tool for Rails: It’s called “Common Core JS.”

The source code is on Github. When you install it, the gem is pulled from RubyGems.

The finished result of the example app we will build today can be seen here. (I recommend you type out each step and only refer to this if you need to.)

It’s based on the idea that you will embrace a common naming convention for your Rails app, will use AJAX rendered-everything (that means all the forms are remote: true), and want a common set of tools for rolling out a quick, dashboard-like app in Rails.

It comes with poor-man’s authentication built-in. Poor man’s auth is safe and works fine, but it isn’t designed for you to grow your entire app on and you should graduate out of if you have any granularity to your access control.

Common Core is a fantastic tool for rapidly building prototypes. It can also be used to create API back-ends for Javascript-heavy apps.

It is a blunt instrument and you should wield it carefully. In particular, you’ll want to remove specific code that it creates because it can create situations where users may have the access they shouldn’t.

Quick Setup

Let’s build the fastest app you can possibly build in Rails.

I’ll call it MyGreatApp, but yours can be named anything of coruse.

rails new MyGreatApp

Once you have the app generated (and even on faster processors Rails new still takes a hot minute or two), go to modify the Gemfile

Add the Gem

gem 'common_core_js'

To your Gemfile.

Then run: bundle install

Setup The Common Core

Then run the Common core install generator (which is implemented as a generator, not a rake task)

bundle exec rails generate common_core:install

Now you’ll create a User objeect, with a migration and model.

do this using. Note that you should not add any fields that will conflict with Devise fields, like email (I’ll add those in the next step).

bundle exec rails generate model User name:string joined_date:date timezone:integer

Add Devise

Add devise to your Gemfile

gem 'devise'

run bundle install, then install devise on the User model:

rails generate devise:install
rails generate devise User

Take a look at the fields on your User database table now. (Here I’m using DB Browser for SQLite)

Notice the fields added name, joined_date, and timezone I’ve put a red box around and the devise fields, including email and encrypted_password, I’ve put a blue box around.

Now you have the most bare-bones Rails app with Devise gem installed. This is great because you get free sign up, login and forgot password fundionality immediately.

Go to

Add jQuery

Add jQuery to your package.json via yarn

yarn add jquery

Go to config/webpack/environment.js and add this code in between the existing two lines

const webpack = require('webpack')
  new webpack.ProvidePlugin({
    $: 'jquery/src/jquery',
    jQuery: 'jquery/src/jquery'

The complete environment.js file looks like so (the part you are adding is shown in red.)

const { environment } = require('@rails/webpacker')

const webpack = require('webpack')
  new webpack.ProvidePlugin({
    $: 'jquery/src/jquery',
    jQuery: 'jquery/src/jquery'

module.exports = environment

Add require("jquery") to your app/javascript/packs/application.js file so it looks like so.

While we are here, let’s also add the common_core javascript too using require("common_core")

The change code is shown in red.


Adding Bootstrap

Next let’s add Boostrap to the Gemfile

gem 'bootstrap', '~> 4'
gem 'font-awesome-rails'

Next delete app/assets/stylesheets/application.css

And replace it completely with a new file


(Do not save the old application.css file or rename and append to it; do not include the contents from the old file in the new .scss file)

@import 'bootstrap';
@import 'font-awesome';
@import 'common_core';

Test it

Now go ahead and start your rails server with bundle exec rails server

Go to /users/sign_up and create a new user account (be sure to enter the same password twice)

You will then be redirected to the Home page, which is now the Ruby on Rails “Yay you’re on Rails.” That’s fine— go ahead and customize your root URL.

Today’s Example App

I’ll make a super-simple system today where Users have many Events An Event belongs to a Format, which in our fictional world is only two choices: Zoom or Outdoor.

Events have a name, a starting datetime, and an ending datetime, and a “publicize” date on which should be before the starting time.

The two datetime fields (starting_at and ending_at) and the date field (publicize_on) can be empty (nil), but if set they are enforced to be: starting_at must be before ending_at. publicize_on must be before starting_at.

An Event will belong_to a Format (class & table). Formats will have a name field and only two records: Zoom and Outdoor. (We can assume they will be id 1 and id 2 in the formats table.)

All Events must belong_to a format, and when we create or edit an Event we can switch its format, but the format cannot be blank (null).

We already have the User object, and we also already have all the login, logout forgot password, and more provided by Devise.

We want the users to log-in and go to a dashboard of their own events.

They should be able to create, edit, & delete their own events with only the validations discussed above.

They should not be able to edit or create events belonging to other users, even by hacking the query parameters.

Finally, the user should be able to edit their own name and timezone, but not any other user’s name or timezone.

Because we want to name our routes from the perspective of the context-interaction, we’ll namespace the controller to Dashboard:: in our Ruby code and /dashboard in the URL. The controller will be at controllers/dashboard and the views will be at views/dashboard

Make the models

Since you already made the User model in the devise setup, let’s go ahead and create the Events and Formats tables.


bundle exec rails generate model Event user_id:integer name:string start_at:datetime end_at:datetime promote_on:date description:string format_id:integer

Then open up the migration file and ed the description line, adding a larger than 256 limit, like 400

Next run bundle exec rake db:migrate to create the table.

Before I go further, let’s edit our models just a bit.

Open models/user.rb and add has_many :events

also add validates_presence_of :name

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable, :trackable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :validatable

  has_many :events
  validates_presence_of :name

Likewise, on the Event object, defined models/event.rb, you’ll need to add the reflexive relationship for belongs_to :user and belongs_to :format

class Event < ApplicationRecord
  belongs_to :user
  belongs_to :format

Now make a formats table

bundle exec rails generate model Format name:string

      invoke  active_record
      create    db/migrate/20200808233939_create_formats.rb
      create    app/models/format.rb
      invoke    test_unit
      create      test/models/format_test.rb
      create      test/fixtures/formats.yml

Modify the migration file to create to dummy Formats, adding this to after end of the create_table block

Because the COVID quarantine prohibits indoor events during 2020, we want to make only two format records: “Zoom” and “Outdoor” events.

Format.create(name: "Outdoor")
Format.create(name: "Zoom")

Your edited migration looks like

class CreateFormats < ActiveRecord::Migration[6.0]
  def change
    create_table :formats do |t|
      t.string :name

    Format.create(name: "Outdoor")
    Format.create(name: "Zoom")

Then run the migration itself, which will now make the table & the two format records.

bundle exec rails db:migrate

-- create_table(:formats)
   -> 0.0025s
== 20200808233939 CreateFormats: migrated (0.0027s) ===========================

Now we have two Formats in our database.

Localized Timezone Support

In order to show dates, we use a localized date display: the date & time is always shown to the user in their own date. To do this you have a few choices: (1) You can save the timezone to the user’s table, and let them set it for themselves, (2) You can show everybody the server’s date

Option #1 – Store timezone On the User object

We already took care of this by adding timezone to our User object.

Option #2 – Use the Server’s Timezone

If the auth object (current_user) does not respond to timezone, the Rails “system clock” will be used. The system clock’s timezone as set by the Rails app is used. This is often the timezone of the headquarter’s of the company that owns the application. (That is, if you do not know the user’s context, you simply use your own company’s context instead.)

Make the Controller, Views & Specs

Next we’re going to do the thing. We’ll make two controllers: Dashboard::EventsController for editing events and Dashboard::UsersController for the user editing their own name.

First, let’s create the Events Controller

rails generate common_core:scaffold Event namespace=dashboard --with-index

A few things to note

  1. Use the ‘generate’ command, not a rake task.
  2. When passing the model name, pass it in the singular form
  3. Here I’ve provided the namespace= with a value of dashboard. You will this is important to how our code comes out.

Here is the heart & soul of the common core: 5 .js.erb files, 5 .haml files, a controller, and a controller spec. Also along for the ride came controllers/dashboard/base_controller.rb as well as views/dashboard/_errors.haml, and layouts/_flash_notices.haml

Take a peak through all the generated code now.

Pay particular attention to _line.haml and _form.haml. You will note _form.haml conveniently is used for both the new/create actions and also for the update action, unifying the layout of your record across CRUD.

You can use both to customize your app quickly and easily.

One more quick step, add this to your routes.rb file.

Make sure to nest the :events route within the :dashboard namespace, as shown here. If you aren’t familiar with namespacing in Rails, check out this blog post on my other blog, The Rails Coach.

Rails.application.routes.draw do
  devise_for :users

  namespace :dashboard do
    resources :events

Start your server with

bundle exec rails server

If the Common Core finds null for timezone on your User object, it will default to either (1) whatever is set for your Rails app in either application.rb or an environment file, or, if don’t have this set (2) the clock timezone of the server that is running your Ruby application.

It’s generally a good idea to set your Rails app timezone to the same timezone of your company’s headquarters, and then don’t change it, because that way if your server happens to move from one timezone to another (for example, you migrate from a server on the East coast to the West coast), your app will be unaffected. If your company changes timezones, you can either leave the Rails app as-is or change it, but be sure to note any place where your default timezone comes through.

config.time_zone = 'Eastern Time (US & Canada)'


We can now do all of these fancy thigns.

Create an event. Leave name or format blank, get an error.

When you create a new event, you must give it a name and Format. Notice how if you don’t, the Rails-side logic will return the form shown with the erroneous fields marked in red.

Edit an Event

Your model-level validations — name and format as required — are enforced in the update action as well.

Deleting An Event

Adding Validation

Add this to your Event class in app/models/event.rb

validate :start_at_before_end_at, if: -> {!start_at.nil? && !end_at.nil?}

def start_at_before_end_at
  if end_at < start_at
    errors.add(:start_at, "can't be after end at")
    errors.add(:end_at, "can't be before start at")

*Validation magic*

Finally, to add validation on all the date fields, here’s our completed Event model

class Event < ApplicationRecord

  belongs_to :user
  belongs_to :format

  validates_presence_of :name

  validate :start_at_before_end_at, if: -> {!start_at.nil? && !end_at.nil?}
  validate :promote_on_before_start_at, if: -> {!promote_on.nil? && !start_at.nil?}

  def start_at_before_end_at
    if end_at < start_at
      errors.add(:start_at, "can't be after end at")
      errors.add(:end_at, "can't be before start at")

  def promote_on_before_start_at
    if start_at < promote_on
      errors.add(:promote_on, "can't be after start at")

Account Dashboard

Next we’re going to create the very simplest of Account Dashboards. Remember that Devise already handles log in, log out, and forgot password, meaning most of the heavy lifting of user authentication has been taken care of.

In this simple app, we want an Account dashboard that let’s us edit only two fields: name and timezone.

First let’s add the route to routes.rb

Rails.application.routes.draw do
  devise_for :users
  # For details on the DSL available within this file, see

  namespace :dashboard do
    resources :events
    resources :users

Next let’s generate some scaffold

rails generate common_core:scaffold User namespace=dashboard

We now instantaly have a very basic dashboard for the User to edit their own details

The final finishing touch here will be to make the Timezone into a drop-down.

To do this, we’ll create a non-AR model :

class UsTimezone
-5 => 'Eastern',
-6 => 'Central',
-7 => 'Mountain',
-8 => 'Pacific',
-10 =>'Hawaii–Aleutian'
def self.all
@@_US_TIMEZONES.collect{|k,v|{label: v, value: k})}

def self.utc_to_name(input) # in hours
utc = input[0...-2].to_i
return @@_US_TIMEZONES[utc]

Next go into the views/dashboard/users/_form.haml and we’re going to make our first cutomization

We’re going to add this:

= f.collection_select(:timezone, UsTimezone.all, :value, :label,  {:prompt => true, value: @user.try(:timezone) }, class: 'form-control')

The full file looks like this

  %div{class: "form-group col-md-4 #{'alert-danger' if user.errors.details.keys.include?(:name)}"}
    = f.text_field :name, value:, size: 256, class: 'form-control', type: ''

  %div{class: "form-group col-md-4 #{'alert-danger' if user.errors.details.keys.include?(:joined_date)}"}
    = date_field_localized(f, :joined_date, @user.joined_date, 'Joined date', current_user.timezone)
  %div{class: "form-group col-md-4 #{'alert-danger' if user.errors.details.keys.include?(:timezone)}"}
    = f.text_field :timezone, value: @user.timezone, size: 256, class: 'form-control', type: ''
  %div{class: "form-group col-md-4 #{'alert-danger' if user.errors.details.keys.include?(:email)}"}
    = f.text_field :email, value:, size: 256, class: 'form-control', type: ''

First, take away the strikethrough text above. This is the text field for the timezone that we don’t want.

In its place, add the new collection_select

  %div{class: "form-group col-md-4 #{'alert-danger' if user.errors.details.keys.include?(:timezone)}"}
    = f.collection_select(:timezone, UsTimezone.all, :value, :label,  {:prompt => true, value: @user.try(:timezone) }, class: 'form-control')

We now have a nice drop-down for our Timezone field. You can replicate this pattern for any field that you want to turn into a drop-down.


Common Core JS harnesses the power of many great things about Rails:

• Database migrations

• ActiveRecord assocations (has_many, belongs_to, etc)

• Scope chains for access control

• Devise for athentication

Remember, make your models first: Add limits and defaults to your database fields by modifying your migrations. Then add the relasionships between the tables using standard ActiveRercord has_many, belongs_to, and has_one.

Then build the common core scaffolding & customize the views and controllers it produces.

With these powerful tools, you can build a dashboard-like app in minutes, complete with simple interface buttons that let your users accomplish most of what they’ll need. The philosophy is that you will want this dashboard as you initially introduce people to your product. The main logic of your application will likely live more in the models, service objects, and domain layer (business logic) parts of your Rails app. For this reason, you are encouraged to customize the files only lightly. (Add some verbiage or change the CSS to customize the look & feel.)

The code you build with common core is cheap and disposable. It is not very modern, but it gets the job done. It is just “good enough” to launch a sophisticated app on, but it isn’t good enough to impress your users with a really good UI.

For that, you’ll want to throw away the front-end code and replace it with a modern JS UI like React, Vue, Ember, or Angular.

By that time, the Common core will have already helped you build (1) a prototype, (2) your business logic, and (3) possibly even some controllers you can re-use (for example, remove the format.js responses and replace them with format.json to change the controllers into a JSON-responding API controller.)

Enjoy your rapid prototyping!

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