Deploying NextJS to Heroku

This took me quite sometime to figure out, so I hope this helps:

  1. Follow Heroku’s instructions on Getting Started on Node.js up until “Deploy the app”
  2. At this point, visiting your site via heroku open will only show an error
  3. Modify your package.json to include the following scripts:
  4. "scripts": {
      // ...
      "heroku-postbuild": "next build",
      "start": "next start -p $PORT"
  5. Push to Heroku again, and voila, it should now work.

Making ActiveRecord associations readonly based on state

My use-case:

* Trip has many destinations and travelers
* Trip states are: 
draft -> checked out -> paid
draft -> checked out -> failed (which should allow them to edit again)

* Trip workflow actually is: 
being edited -> for confirmation -> go to payment gateway (set to checked out) -> go back to success/fail
payment gateway sends payment details to system whether payment was success (paid) or failed (failed)

To disable editing on trip:

class Trip < ApplicationRecord
  def readonly?

  def draft?

  def checked_out?
    return false if checked_out_on_changed?
    # this is required, otherwise saving the relations will always fail
    # as draft will always return false even during the saving process

To disable changes on related records (destination/traveler):

class Destination < ApplicationRecord
  validate :trip_is_in_draft

  def trip_is_in_draft
    errors.add(:trip, "should be in draft") if !trip.draft?

Testing Email Deliveries using Cucumber/Capybara/Minitest

# features/support/env.rb
Around('@email') do |scenario, block|
  ActionMailer::Base.delivery_method = :test
  ActionMailer::Base.perform_deliveries = true

  old_adapter = ActiveJob::Base.queue_adapter
  ActiveJob::Base.queue_adapter = :inline
  # ActiveJob::Base.queue_adapter.perform_enqueued_jobs = true

  ActiveJob::Base.queue_adapter = old_adapter

# features/steps/*_step.rb

Then(/^I should receive an email$/) do
  # assuming mailcatcher
  assert_difference -> { ActionMailer::Base.deliveries.length } do
    # do stuff that is supposed to send an email

# features/*.feature

Scenario: Checkout page
  When I press the checkout button
  Then I should receive an email

Removing field name from validation error message

Related to the accepted answer and another answer down the list:

I’m confirming that nanamkim’s fork of custom-err-msg works with Rails 5, and with the locale setup.

You just need to start the locale message with a caret and it shouldn’t display the attribute name in the message.

A model defined as:

class Item < ApplicationRecord
  validates :name, presence: true

with the following en.yml:

              blank: "^You can't create an item without a name."

item.errors.full_messages will display:

You can't create an item without a name

instead of the usual

Name You can't create an item without a name

How to create a PORO model and use it in Rails Form Helpers

First off, I’ll start with our use-case:

We have a fairly simple form for an item with some complexity. It would have default values derived from the current_user‘s attributes but would still have the field on its own. Overriding it in Item model feels like overkill (and starts to be a violation of SRP) so we set out to create a PORO model for it. Full code and explanation below the fold.

Continue reading How to create a PORO model and use it in Rails Form Helpers

Thoughts on RailsConf 2016 – ActiveRecord vs. Ecto: A Tale of Two ORMs by Brad Urani

Everything he showed can be done using AR. It’s not anymore the “established pattern” of using AR, but by all means it’s possible to achieve the same kind of results (e.g. moving validations to specific methods and using explicit queries instead of chainable scopes) but it requires more discipline – because Rails just spoils all Rails developers with all the conveniences that it provides, me included.

Maybe I’ll do an experiment one of these days of ripping AR out of Rails and using either Ruby Object Mapper or Sequel.

Rails Generator Gotcha

Note to self:

Remove devise_for in routes.rb if you’re trying to generate a scaffold of an already existing model.

Steps to replicate:

  1. rails g model Foo name
  2. rails g devise Foo
  3. rails g scaffold Foo –skip
    1. This would result with the error: The name ‘Foo’ is either already used in your application or reserved by Ruby on Rails. Please choose an alternative and run this generator again.

Commenting the devise_for line in routes.rb will allow you to proceed with the scaffold.

Minitest with Kaminari

While converting my tests from FactoryGirl.create to FactoryGirl.build_stubbed, I ran into trouble with Kaminari. Here’s how I fixed it.


Kaminari functions by adding .page() (and some other methods) at the end of your ActiveRecord call chain. A typical example of paginating via Kaminari is as follows:

class UsersController < ApplicationController
  def active_users
    @users =[:page])

This is a problem when you’re trying to stub out the return of the AR call to return an array. Here’s a corresponding test that would fail:

require 'test_helper'

describe UsersController, "#active_users" do
  test "success" do
    users = FactoryGirl.build_list :user, 3
    get :search, term: "admin_user"
    assert_response :success

Because users is just a regular array here, and Kaminari tries to call .page() on the array, it would fail with a NoMethodError: undefined method `page’ for # because Array#page isn’t defined.

Trying to stub out .page() by users.stubs(page: users) would give you ActionView::Template::Error: undefined method `model_name’ for #. And so on, as long as you’re using Kaminari-specific methods.

The solution

The solution is pretty simple (but took me 2+ hours to research). Call Kaminari.paginate_array on the FactoryGirl.build_list.

users = Kaminari.paginate_array FactoryGirl.build_list :user, 3

From the documentation:

Kaminari::paginate_array method converts your Array object into a paginatable Array that accepts page method.

For now, I’m putting the Kaminari.paginate_array inside the test, but long term, it makes sense to put it in the controller code. This way, even if we change to return an array, no other code would break. Then again, that’s why we have tests, right?

Using Dropbox Chooser within ActiveAdmin

We use Dropbox quite heavily in Loudcloud. I’m working on an internal CRM system and since all of our files are on Dropbox anyway, I figured it would be super helpful to just have to link to our Dropbox files.

Here are the relevant files:

# app/inputs/dropbox_input.rb
class DropboxInput < Formtastic::Inputs::FileInput
  def to_html
    input_wrapping do
      label_html <<
      builder.text_field(method, input_html_options.merge({ type: "dropbox-chooser", style: "visibility: hidden;" }))

# app/admin/invoice.rb
ActiveAdmin.register Invoice do
  form do |f|
    within @head do
      script src: "", id: "dropboxjs", type: "text/javascript", "data-app-key" => "APP_KEY_HERE"

    # ....

    f.inputs "Official Receipt" do
      f.input :or_file_url, as: :dropbox, label: "OR File URL"

    # ....


Nested forms with polymorphic association in Active Admin/Formtastic

I spent nearly the whole day making this work.

Given models:
Invoice, has_many :items
Item belongs_to :itemizable, polymorphic: true
Domain & Service has_many :items, as: :itemizable

The problem was multiple things:

  1. The automagic of Formtastic can’t detect the collection if it’s a polymorphic association
  2. Formtastic doesn’t really play well with non-existent attributes

Initially, I’ve thought of just doing:

ActiveAdmin.register Invoice do
  form do |f|    
    # ...
    f.has_many :items do |item|
      item.input :itemizable, collection: (Domain.all + Service.all)
      item.input :quantity
      item.input :price_per_piece


But this fails because 1) domains and service can share the same id and 2) I have no way to tell what the item was.
A few hours in and I was going nowhere. It’s surprisingly hard to look for anything related to polymorphic associations on Formtastic. This post gave me an idea however.

So, I’ve thought, why not just hold the id temporarily on an accessor attribute and just do the assignment from a callback before validation kicks in based on which attribute it went into? Raise an error if both were filled up.

It worked! I can now save new polymorphic records. (look at Item#assign_itemizable)

There’s a small problem however. The form to edit an existing record doesn’t pre-populate the corresponding select dropdowns. The solutions was rather simple, override the reader method to return the id of the itemizable if the itemizable is a member of the class.

Maintenance-wise, everything here would add overhead for every new itemizable model I would associate to item, but overall, I think it was a pretty elegant hack. *pats self at back*

Here’s the complete code:

# app/models/invoice.rb
class Invoice < ActiveRecord::Base 
  has_many :items

  accepts_nested_attributes_for :items

# app/models/item.rb
class Item < ActiveRecord::Base
  before_validation :assign_itemizable

  belongs_to :invoice
  belongs_to :itemizable, polymorphic: true
  validates :itemizable, presence: true

  attr_accessor :itemizable_domain, :itemizable_service

  def itemizable_domain if self.itemizable.is_a? Domain

  def itemizable_service if self.itemizable.is_a? Service

  def assign_itemizable
    if [email protected]ble_domain.blank? && [email protected]_service.blank?
      errors.add(:itemizable, "can't have both a domain and a service") 

    unless @itemizable_domain.blank?
      self.itemizable = Domain.find(@itemizable_domain)

    unless @itemizable_service.blank?
      self.itemizable = Service.find(@itemizable_service)

# app/admin/invoice.rb
ActiveAdmin.register Invoice do
  form do |f|
    f.inputs "Invoice" do 
      f.input :customer
      f.input :invoice_number
      f.input :issuing_person
      f.input :issued_on
      f.input :remarks
    f.has_many :items do |item|
      item.input :itemizable_domain, collection: Domain.all
      item.input :itemizable_service, collection: Service.all
      item.input :quantity
      item.input :price_per_piece


Edit: Fixed a bug in Item because I overwrote the accessors, which were being called in the validation. This caused a sort of chicken-egg situation, and ultimately causes the validation to fail all the time. Changed .empty? to .blank? so it doesn't barf out on nils.