Since Rails 6.1, if we use where.not with multiple attributes, it applies logical NAND (NOT(A) OR NOT(B)) instead of NOR (NOT(A) AND NOT(B)). If you do not take care, this change will increase the matched set.

Examples

"Don't send newsletters neither to admins nor to trashed users!" becomes "Don't send newsletters to trashed admins".

User.where.not(role: 'admin', trashed: true)
# Before Rails 6.1, with NOR
=> "SELECT "users".* FROM "users" WHERE "users"."role" != 'admin' AND "users"."trashed" != TRUE"
# Equivale...

You can use RSpec::Matchers.define_negated_matcher to define a negated version of an existing matcher. This is particularly useful in composed matcher expressions or to create more expressive and meaningful matchers.

You should only negate "atomic" matchers with an unambiguous inversion. For example, have_radio_button(label) can be negated, whereas have_active_radio_button(label) should not be. Its inversion could either mean "there is a radio button with that label, but it is not active", or "there is no radio button with that la...

In my case [...] the catalog is an XML that contains all kinds of possible products, categories and vendors and it is updated once a month. When you read this file with the Nokogiri default (DOM) parser, it creates a tree structure with all branches and leaves. It allows you to easily navigate through it via css/xpath selectors.

The only problem is that if you read the whole file into memory, it takes a significant amount of RAM. It is really ineffective to pay for a server if you need this RAM once a month. Since I don't need to n...

TL;DR When using Cache-Control on a Rails application, make sure the Vary: Accept header is set.

Proxy caching is a good feature to serve your publicly visible application content faster and reduce load on your servers. It is e.g. available in nginx, but also affects proxies delivered by ISPs.

Unfortunately, there is a little problem in Rails < 6.1 when delivering responses for different MIME-types. Say you have an arbitrary route in your Rails application that is able to respond with regular HTML and JSON. By sending the specific ...

Field error steps

Spreewald's The ... field should have an error and The ... field should have the error ... steps now have built-in support for Rails and Bootstrap (v3-v5) error classes. When using Bootstrap, it is no longer necessary to overwrite the steps in your project.

At the same time, support for formtastic has been removed as there were no real use cases. Due to that, no breaking change was introduced, as the amount of users affected by this should be zero (it was neither in the documentation nor tested).

Users may now add...

The Interactive Advertising Bureau (IAB) is a European marketing association which has introduced a standard how advertising can be served to users in line with the General Data Protection Regulation (GDPR). This standard is called the TCF 2.0 (Transparency and Consent Framework). If you want to integrate any kind of advertising into a website, chances are the advertising network will require your website to implement that standard. This is a very brief overview of what this means:

The basic idea in the TCF 2.0 ...

Rails 6.1 has a "strict loading" mode that forces the developer to preload any association they plan to use. Associations no longer load lazily. An error is raised when reading an association that was not preloaded.

Enabling strict loading is a tool to prevent n+1 queries.

Strict loading can be enabled for individual records, for a single association,...

A flaky test is a test that is often green, but sometimes red. It may only fail on some PCs, or only when the entire test suite is run.

There are many causes for flaky tests. This card focuses on a specific class of feature with heavy side effects, mostly on on the UI. Features like the following can amplify your flakiness issues by unexpectedly changing elements, causing excessive requests or other timing issues:

• Lazy loading images
• Autocomplete in search f...

This RailsCast demonstrated a very convenient method to activate VCR for a spec by simply tagging it with :vcr.

For RSpec3 the code looks almost the same with a few minor changes. If you have the vcr and webmock gems installed, simply include:

# spec/support/vcr.rb
VCR.configure do |c|
  c.cassette_library_dir = Rails.root.join("spec", "vcr")
  c.hook_into :webmock
end

RSpec.configure do |c|
  c.around(:each, :vcr) do |example|
    name = example.metadata[:full_descripti...

You want to use <input type="number"> fields in your applications.
However, your desktop users may encounter some weird quirks:

1. Aside from allowing only digits and decimal separators, an "e" is also allowed (to allow scientific notation like "1e3").
   • Non-technical users will be confused by this.
   • Your server needs to understand that syntax. If it converts only digits (e.g. to_i in Ruby) you'll end up with wrong values (like 1 instead o...

Event delegation is a pattern where a container element has a single event listener that handles events for all descendants that match a CSS selector.

This pattern was popularized by jQuery that lets you do this:

$('.container').on('click', '.message', function(event) {
  console.log("A message element was clicked!")
})

This technique has some advantages:

1. When you have many descendants, you save time by only registering a single listener.
2. When the descendants are changed dynamic...

Sometimes a link or input field has no visible label. E.g. a text field with a magnifying glass icon 🔎 and a "Search" button does not really need a visible label "Query".

For accessibility reasons it is good practice to give such a field an [aria-label] attribute:

<input type="search" aria-label="Search contacts">

This way, when a visually impaired user focuses the field, the screen reader will speak the label text ("Search contacts").

Info

Without an `[aria-...

git --fixup is very handy to amend a change to a previous commit. You can then autosquash your commits with git rebase -i --autosquash and git will do the magic for you and bring them in the right order. However, as git --fixup wants a ref to another commit, it is quite annoying to use since you always have to look up the sha of the commit you want to amend first.

Inspired by the [shortcut to checkout recent branches with fzf](https://makandracards.com/makandra/505126-g...

We are using Spring in our tests for sequential test execution but not for parallel test execution. And Rails requires you to set the config.cache_classes = false if you are using Spring in tests.

With our setup, this would raise the following error in cucumber-rails for parallel test executions due to some legacy database cleaner issue.

WARNING: You have set Rails' config.cache_classes to false
    (Spring needs cache_classes set to false). This is known to cause probl...

It is generally discouraged to load your JavaScript by a <script src> tag in the <head>:

<head>
  <script src="app.js"></script>
</head>

The reason is that a <script src> tag will pause the DOM parser until the script has loaded and executed. This will delay the browser's first contentful paint.

A much better default is to load your scripts with a <script src defer> tag:

<head>
  <script src="app.js" defer></script>
</head>

A deferred script has many useful properties:

• I...

The attached compiler() function below applies JavaScript behavior to matching HTML elements as they enter the DOM.

This works like an Unpoly compiler for apps that don't use Unpoly, Custom Elements or any other mechanism that pairs JavaScript with HTML elements.

The compiler() function is also a lightweight replacement for our legacy [$.unobtrusive()](https://makandracards.com/makandra/4-unobtrusiv...

We had a card that described how to install multiple mysql versions using mysql-sandbox. Nowadays with the wide adoption of docker it might be easier to use a MySQL docker image for this purpose.

Create a new mysql instance

docker run --name projectname_db -e MYSQL_ROOT_PASSWORD=secret -p "33008:3306" -d --restart unless-stopped mysql:5.7

The port 33008 is a freely chosen free port on the host machine that will be used to establish a...

The Node Version Manager allows installing multiple NodeJS versions and switching between them.
By default, it does not automatically switch versions when entering a directory that holds a .nvmrc file.

The project's readme document offers a bash function which calls nvm use after each cd. In fact, it replaces cd in your bash.

I did not want to do that, but instead use the $PROMPT_COMMAND feature. So here is my take on it.
Note that it is much shorter, it probably does a f...

The linked article points out that COUNT queries might be unexpectedly slow in PostgreSQL.

If you just need to know "are there any records" use any?. This uses SELECT 1 AS one FROM ... LIMIT 1 under the hood.
If you just need to know "are there no records" use empty? or none?. This uses SELECT 1 AS one FROM ... LIMIT 1 under the hood.

In short: Replace foo.count > 0 with foo.any? or foo.count == 0 with foo.none?

If you require quick counts and can tolerate some level of imprecision, consider exploring the ...

When testing JavaScript functionality in Selenium (E2E), you may need to access a class or function inside of a evaluate_script block in one of your steps. Capybara may only access definitions that are attached to the browser (over the window object that acts as the base). That means that once you are exporting your definition(s) in Webpacker, these won't be available in your tests (and neither in the dev console). The following principles/concepts also apply to Sprockets.

Say we have a StreetMap class:

// street_map.js
class S...

Table of content for the linked article:

1. The `loading=lazy` attribute
2. Email, call, and SMS links
3. Ordered lists `start` attribute
4. The `meter` element
5. HTML Native Search
6. Fieldset Element
7. Window.opener
8. Base Element
9. Favicon cache busting
10. The `spellcheck` attribute
11. Native HTML sliders
12. HTML Accordion
13. `mark` tag
14. `download` attribute
15. Performance tip
16. Video thumbnail
17. input type="search"

I encountered a unlucky behavior of byebug 11.1.3 (the most recent version at time of writing) when using it with Rails 6 and it's new autoloading component, zeitwerk. There already is a issue for that, so I hope it will be fixed with a future release.

The following test succeeds:

  context 'factories' do
    let(:test_case) { FactoryBot.create(:test_case) }
    it 'are valid' do
      expect(test_case).to be_valid
    end
  end

But when I did the same in byebug the foll...

rspec >= 3.1 brings a method and_wrap_original. It seems a bit complicated at first, but there are use cases where it helps to write precise tests. For example it allows to add expectations on objects that will only be created when your code is called.

If you have older rspec, you could use expect_any_instance_of, but with the drawback, that you can't be sure if it really was the correct instance which got the message.

Example

The example model uses different validators based on a flag:

class MyModel < ApplicationRecord

 ...

The usual way to build a relation in a ActiveSupport::Concern is this:

module MyModule
  extend ActiveSupport::Concern

  included do
    scope :disabled, -> { where(disabled: true) }
  end

end

However, if you have a association with a polymorphic model, where you have to select based on the kind of record, using included like this will not produce the wanted results:

module MyModule
  extend ActiveSupport::Concern

  included do
    has_many :tasks,
      ->...