HOWTOs for Ruby on Rails and JavaScript

Ruby: You can nest regular expressions

Ruby lets you re-use existing RegExp objects by interpolating it into new patterns:

locales_pattern = /de|en|fr|es/i

html_tag_pattern = /<html lang="#{locales_pattern}">/

Any modifiers like /i or /x will be preserved within the interpolated region, which is pretty cool. So in the example above only the interpolated locales are case-insensitive, while the pattern around it (/<html .../) remains case-sensitive.

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routing-filter is broken with Rails 7.1

If you are using the routing-filter gem in your Rails 7.1 app for managing URL segments for locales or suffixes, you will notice that the filters do no longer apply, routes are broken and the necessary parameters are no longer extracted. That is because routing-filter patches Rails' find_routes-method to get the current path and apply its defined filters on it. These filters then modify the params that are handed over to your controller action. This way you receive a locale parameter from a ...

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Active Record: Never use optional with a symbol, lambda or proc

tl;dr

Do not use the option optional on association declarations with a symbol, lambda or proc.

Explanation

Association declarations like belongs_to support the option optional. This option does not support symbols, lambdas or procs. If you do so, this will always result in optional: true. So your records can miss a presence validation if optional is used with a symbol, lambda or proc.

If you set t...

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Bash script to list git commits by Linear ID

As we're switching from PT to Linear, I've updated the existing bash script to work for commits that are referencing Linear IDs.

A core benefit of our convention to prefix commits by their corresponding issue ID is that we can easily detect commits that belong to the same issue. You can either do that manually or use the bash script below. It can either be placed in your .bashrc or a...

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Ruby: How to use global variables for a conditional debugger

You can share a state in Ruby with global variables. Even if you should avoid them whenever possible, for debugging an application this could be temporary quite handy.

Example:

class User

  after_save { byebug if $debug; nil }

  def lock
   self.locked = true
   save
  end

end

Rspec.describe User do

  let(:user) { create(:user) } 

  before do
   # Many users are created and saved in this hook, but we don't want the debugger to stop for them...

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Heads up: Sidekiq per default silently fails when retries are exhausted!

For Sidekiq to be able to retry your jobs it has to be able to catch errors that occur while a job is executed.

Per default, Sidekiq will not raise / notify you if the retry count is exhausted. It will only copy the job to the dead queue (see wiki).

If you want to get notified, you have to implement it in your worker explicitly with a sidekiq_retries_exhausted-block, e.g. like this:

class DownloadWorker
  include Sidekiq::Worker

  # Import jobs are retried a few time...

github.com

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RSpec: Using helpers in view specs

If an view spec crashes due to undefined helper methods, you can enable this option:

# config/application.rb
config.action_controller.include_all_helpers = true

If you cannot use this setting, your spec can include individual helper modules like this:

describe 'some view', type: :view do
  helper SomeHelper
  helper OtherHelper

  it 'renders' do
    render 'view_that_uses_helpers'
  end
end

Alternatively you can also explicitly include *all help...

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Rails: Integrating shoelace components

shoelace is a library of web components. Here is a proof of concept how a integration (slightly different as the official docs for Rails) might look like in Rails + webpack + Unpoly. Also see the HN discussion for pro and cons.

preview.gif preview.mp4

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Capybara: Quick checking for element presence (without retries or timeout)

Element finding is a central feature of Capybara. Since #find is normally used to get elements from the current page and interact with them, it's a good thing that some Capybara drivers (e.g. Selenium) will wait an amount of time until the expected element shows up. But if Capybara cannot #find it at all, you'll get an error.

if page.find('.that-element')
  # Do something
else
  # Never happens because #find raises
end

In order to simply check whether an element is present, without errors raised, you can use #has_css?. It...

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Nested ActiveRecord transaction pitfalls

When working with custom transactions and use ActiveRecord::Rollback you may encounter unexpected behaviour if you try to roll back your changes.

tl;dr

When using nested transactions, ActiveRecord::Rollback might not do what you expect, since it will only roll back the inner, but not the outer transaction.

You can fix this behavior by using transaction(joinable: false) but this leads to a bunch of different problems.

When you don't need an explicit ActiveRecord::Rollback, don't worry about any of this and just use a plan `tran...

api.rubyonrails.org

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Capybara: Find an element that contains a string

There is no CSS selector for matching elements that contains a given string ¹. Luckily, Capybara offers the :text option to go along with your selector:

page.find('div', text: 'Expected content')

You can also pass a regular expression!

page.find('div', text: /Expected contents?/i)

Note that if your CSS selector is as generic as div, you might get a lot more results than you expect. E.g. a <div class="container"> that surrounds your entire layout will probably also contain that text (in a descendant) and ...

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Always convert and strip user-provided images to sRGB

Debugging image color profiles is hard. You can't trust your eyes in this matter, as the image rendering depends on multiple factors. At least the operation system, browser or image viewer software and monitor influence the resulting image colors on your screen.

When we offer our users the possibility to upload images, they will most likely contain tons of EXIF metadata and sometimes exotic color profiles like eciRGB. We want to get rid of the metadata, as it might contain sensitiv...

lenna_converted.jpg lenna_ecirgb.jpg lenna_without_profile.jpg

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Ruby: How to determine the absolute path relative to a file

If you want to get the path of a file relative to another, you can use the expand_path method with either the constant __FILE__ or the method __dir__. Read this card for more information about __FILE__ and __dir__.

Example

Structure:

.
├── bin
│   ├── format_changelog
├── CHANGELOG.md

bin/format_changelog:

#!/usr/bin/env ruby

changelog_path = ? # How to get the path to ../CHANGELOG.md independent of the working dir of the caller
changelog = File.read(changelog_path)

# ... further actions...

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Using ngrok for exposing your development server to the internet

Sometimes you need to access a dev server running on localhost from another machine that is not part of the same network. Maybe you want to use your phone to test a web page, but are only in a guest WiFi. In the past, we often used some port forwarding or other techniques to expose the service to the internet.

Enter ngrok, a command line tool that gives you an on-the-fly internet...

ngrok.png

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makandra cards: A knowledge base on web development, RoR, and DevOps

What is makandra cards?

We are makandra, a team of 60 web developers, DevOps and UI/UX experts from Augsburg, Germany. We have firmly anchored the sharing of knowledge and continuous learning in our company culture. Our makandra cards are our internal best practices and tips for our daily work. They are read worldwide by developers looking for help and tips on web development with Ruby on Rails and DevOps.

15 years ago – in 2009 – we wrote our first card. Since then, over 6000 cards have been created, not o...

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Rails: Using require and permit for attributes

Raising errors for required and permitted attributes makes it easier to find errors in your application during development and in tests. Consider this approach if you want to strengthen the params handling in your application.

Example

config.action_controller.action_on_unpermitted_parameters = :raise

def user_params
  params.require(:user).permit(:full_name)
end

Effects

This raises an error `ActionController::Parameter...

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Unpoly + Nested attributes in Rails: A short overview of different approaches

This card describes two variants, that add a more intuitive workflow when working with nested attributes in Rails + Unpoly.

Example

For the following examples we use a simple data model where a user has zero or more tasks.

class ExampleMigration < ActiveRecord::Migration[7.1]
  def change
    create_table :users do |t|
      t.string :full_name
      t.timestamps
    end

    create_table :tasks do |t|
      t.string :title
      t.references :user
      t.timestamps
    end
  end
end

class Task < ApplicationRecord
...

image_2.gif image_3.gif image.gif

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Collect all values for a given column in an ActiveRecord scope

In modern Rails versions you can also use ActiveRecord's pluck method.

User.active.pluck(:id)
=> [1, 5, 23, 42]

If you are plucking from the id column in particular you can also say:

User.active.ids
=> [1, 5, 23, 42]

For a DISTINCT selection, use distinct on your scope (not the resulting array).

Article.distinct.pluck(:state)
...

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Testing ActiveRecord callbacks with RSpec

Our preferred way of testing ActiveRecord is to simply create/update/destroy the record and then check if the expected behavior has happened.

We used to bend over backwards to avoid touching the database for this. For this we used a lot of stubbing and tricks like it_should_run_callbacks.

Today we would rather make a few database queries than have a fragile test full of stubs.

Example

Let's say your User model creates a first Project on cr...

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Bookmarklet to generate a commit message for an issue in Linear.app

Your commit messages should include the ID of the issue your code belongs to.
Our preferred syntax prefixes the issue title with its ID in brackets, e.g. [FOO-123] Avatars for users.
Here is how to generate that from an issue in Linear.

Add a new link to your browser's bookmarks bar with the following URL.

javascript:(() => {
  if (document.querySelector('[data-view-id="issue-view"]')) {
    const [id, ...words] = document.title.split(' ') ;
    prompt('Commit message:', `[${id}] ${words.join(' ')}`)
  } else {
    alert('Open issue...

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Bash: Build and execute command lines on the fly with "xargs"

xargs is a powerful bash tool that can take input from $STDIN and pass it to a given command. I.e. you can do the following:

$> cat tmp/parallel_cucumber_failures.log
features/authentication.feature:33
features/backend/pages.feature:5
features/backend/pages.feature:60

$> cat tmp/parallel_cucumber_failures.log | xargs geordi cucumber
# Running features
> Only: features/authentication.feature:33 features/backend/pages.feature:5 features/backend/pages.feature:60
...

Beside the linked article you might also be interested in reading ...

web.archive.org

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JavaScript basics tutorial: 33 Concepts Every JavaScript Developer Should Know

This repository was created with the intention of helping developers master their concepts in JavaScript. It is not a requirement, but a guide for future studies. It is based on an article written by Stephen Curtis.

Call Stack
Primitive Types
Value Types and Reference Types
Implicit, Explicit, Nominal, Structuring and Duck Typing
== vs === vs typeof
Function Scope, Block Scope and Lexical Scope
Expression vs Statement
IIFE, Modules and Namespaces
Message Queue and Event Loop
setTimeout, setInte...

github.com

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Regular Expressions: Quantifier modes

When you repeat a subpattern with a *, + or {...} operator, you may choose between greedy, lazy and possessive modes.

Switching modes may affect the result and performance of your regular expressions. In the worst case, an ill-suited mode may make your regular expression so slow that it can DoS your application (Examples are the ActiveRecord's PostgreSQL CVE-2021-22880 or the [Cloudflare outage 2019](https://makandracards.com/makandra/77515-regular-expressions-excessive-backtracking...

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Rails: Comparison of assignable_values and Active Record enum types

We are using assignable_values for managing enum values in Rails. Nevertheless Rails is adding more support for enum attributes, allowing to have a closer look at the current feature set in comparison to our still preferred option assignable_values.

Active Record enum attribute interface

By default Rails is mapping enum attributes to integers:
...

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tl;dr

Explanation

tl;dr

Example

What is makandra cards?

Example

Effects

Example

Example

Table of Contents

Active Record enum attribute interface