It might sometimes be useful to check whether your Rails application accesses the file system unnecessarily, for example if your file system access is slow because it goes over the network.

The culprit might be a library like carrierwave that checks file existence or modification times, whereas your application could determine all this from your database.

Introducing strace

One option it to use strace for this, which logs all system calls performed by a process.

To do this, start your rails server using something like

DISA...

Testing file download links in an end-to-end test can be painful, especially with Selenium.

The attached download_helpers.rb provides a download_link method for your Capybara tests. It returns a hash describing the download's response:

details = download_link('Download report')
details[:disposition]  # => 'attachment' or 'inline'
details[:filename]     # => 'report.txt'
details[:text]         # => file content as string
details[:content_type] # => 'text/plain'

Features

Compared to [other approaches](...

There is a way to use multiple databases in Rails.
You may have asked yourself how you're able to keep your test databases clean, if you're running multiple databases with full read and write access at the same time. This is especially useful when migrating old/existing databases into a new(er) one.

Your database.yml may look like this:

default: &default
  adapter: postgresql
  encoding: unicode
  username: <%= ENV['DATABASE_USER'] %>
  host: <%= ENV['DATABASE...

tl;dr
You can use attribute? as shorthanded version of attribute.present?, except for numeric attributes and associations.

Technical Details

attribute? is generated for all attributes and not only for boolean attributes.

These methods are using #query_attribute under the hood. For more details you can see ActiveRecord::AttributeMethods::Query.

In most circumstances query_attribute is working like attribute.present?. If your attribute is responding to :zero? then you have to be aware that `query_attri...

You can use Unpoly's up.on with a named listener function and immediately unbind this event listener with { once: true }:

up.on('up:fragment:inserted', { once: true }, function () { ... })

In Unpoly 1 you can immediately unregister the listener with up.off:

up.on('up:fragment:inserted', function fragmentInsertedCallback() {
  up.off('up:fragment:inserted', fragmentInsertedCallback)
  // ... code for the callback function, which should run only once
})

Exam...

tl;dr: Use the URLSearchParams API to make your live easier if you want to get or manipulate query parameters (URL parameters).

URLSearchParams API

The URLSearchParams API is supported in all major browsers except IE 11.

It offers you a bunch of useful methods:

• URLSearchParams.append() - appends a query parameter
• URLSearchParams.delete() - deletes the specified query parameter
• URLSearchParams.get() - returns the value of the specified query parameter
• `URLSearchP...

Redis.current will be removed without replacement in redis-rb 5.0.
Version 4.6.0 adds deprecation warnings for Redis.current and Redis.current=:

`Redis.current=` is deprecated and will be removed in 5.0.

If your application still uses Redis.current, you can only fix it by no longer using it. Here is how.

Redis.new when you need it

You can easily instantiate a Redis client when you need it.

There is probably already a constant like REDIS_URL that you use to configure Sidekiq or similar. So just use that one.

``...

RSpec's let allows you to super into "outside" definitions, in parent contexts.

Example:

describe '#save' do
  subject { described_class.new(attributes) }
  let(:attributes) { title: 'Example', user: create(:user) }

  it 'saves' do
    expect(subject.save).to eq(true)
  end

  context 'when trying to set a disallowed title' do
    let(:attributes) { super().merge(title: 'Hello') } # <==

    it 'will not save' do
      expect(subject.save).to eq(false)
    end
  end
end

I suggest you don't make a habit of using this regula...

Sometimes we write plain SQL queries in migrations so we don't have to mock ActiveRecord classes. These two migrations do the same:

class Migration1 < ActiveRecord::Migration[5.2]
  class User < ActiveRecord::Base; end

  def up
    add_column :users, :trashed, :boolean
    
    User.update_all(trashed: false)
  end
end

class Migration2 < ActiveRecord::Migration[5.2]
  def up
    add_column :users, :trashed, :boolean

    update("UPDATE users SET trashed = #{quoted_false}")
  end
end

The plain SQL migration is less code, but h...

When using where.not with a Hash of multiple attributes, Rails applies logical NAND (NOT (A AND B)).

This contrasts with logical NOR (NOT A AND NOT B), which is achieved by chaining multiple where.not calls.

The difference in logic alters the scope of excluded records:

• NAND: Excludes records only if they match all attributes simultaneously.
• NOR: Excludes records if they match any of the attributes.

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...