Rails 5.2+ supports "verbose query logs" where it shows the source of a query in the application log.
Normally, it looks like this:

  User Load (0.5ms)  SELECT "users".* FROM "users" WHERE ...
  ↳ app/controllers/users_controller.rb:42:in `load_users'

However, you may encounter ActiveRecord's LogSubscriber as the source for all/most queries which is not helpful at all:

  User Load (0.5ms)  SELECT "users".* FROM "users" WHERE ...
  ↳ activerecord (6.0.3.3) lib/active_record/log_subscriber.rb:100:in `debug'

While th...

Learn how to create offline applications with service workers.

1. The amazing power of service workers
2. Writing your first service worker with vanilla JS
3. Saving recently viewed pages offline with service workers and vanilla JS
4. Offline first with service workers and vanilla JS
5. Improving web font performance with service workers
6. How to set an expiration date for items in a service worker cache
7. How to update a service worker
8. How to trigger a service worker function from the front end with vanilla JS
9. How to immediately ...

When you use Sentry to monitor exceptions, an important feature is Sentry's error grouping mechanism. It will aggregate similar error "events" into one issue, so you can track and monitor it more easily. Grouping is especially important when you try to silence certain errors.

It is worth understanding how Sentry's grouping mechanism works.

The default grouping mechanism

The exact algorithm has changed over time, and Sentry will keep using the algorithm t...

Chrome has a built-in utility to check performance and accessibility (and more) of your web app: Lighthouse.

Open the Developer Tools and go to the lighthouse tab:

Then you'll see some suggestions on how to improve your site.
This is cool, because you can even use it with non-public pages or your development environment (but be aware that some settings we're using for development, like not minifying JS and CSS files, might ruin your stats)...

Rails middlewares are small code pieces that wrap requests to the application. The first middleware gets passed the request, invokes the next, and so on. Finally, the application is invoked, builds a response and passes it back to the last middleware. Each middleware now returns the response until the request is answered. Think of it like Russian Dolls, where each middleware is a doll and the application is the innermost item.

You can run rake middleware to get the ordered list of used middlewares in a Rails application:

$> rake midd...

If you want to prevent that two processes run some code at the same time you can use the gem with_advisory_lock.

What happens

1. The thread will wait indefinitely until the lock is acquired.
2. While inside the block, you will exclusively own the advisory lock.
3. The lock will be released after your block ends, even if an exception is raised in the block.

This is usually required if there is no suitable database row to lock on.

Example

You want to generate a...

grep is the go-to CLI tool to accomplish tasks like filtering large files for arbitrary keywords. When additional context is needed for search results, you might find yourself adding flags like -B5 -A10 to your query. Now, every search result covers 16 lines of your bash.

There is another way: You can easily pipe your search results to the VIM editor and cycle through them.

Example: Searching for local occurrences of "User"

vim -q <(grep -Hn -r "User" .)

# vim -q starts vim in the "quickfix" mode. See ":help quickfix"
# grep...

If you migrate a Rails application from Sprockets to Webpack(er), you can either transpile your CoffeeScript files to JavaScript or integrate a CoffeeScript compiler to your new process. This checklist can be used to achieve the latter.

1. If you need to continue exposing your CoffeeScript classes to the global namespace, define them on window directly:

-class @User
+class window.User

2. Replace Sprocket's require statement with Webpacker's...

Grundidee

CSP hat zum Ziel einen Browser-seitigen Mechanismus zu schaffen um einige Angriffe auf Webseiten zu verhindern, hauptsächlich XSS-Angriffe.

Einschub: Was ist XSS?

XSS = Cross Site Scripting. Passiert wenn ein User ungefiltertes HTML in die Webseite einfügen kann.

<div class="comment">
  Danke für den interessanten Beitrag! <script>alert('you have been hacked')</script>
</div>

Rails löst das Problem weitgehend, aber

• Programmierfehler weiter möglich
• manchmal Sicherheitslücken in Gems oder Rails

Lösungsid...

GoodJob is a new background worker gem. It's compatible with ActiveJob.

We're huge fans of Sidekiq for its stability and features. One advantage of GoodJob over Sidekiq is that GoodJob doesn't require Redis. So in cases where you don't have Redis or don't want to pay for a Redis HA quorum node, this might be an alternative worth checking out.

"Open-source software (OSS) is great. Anyone can use virtually any open-source code in their projects."

Well, it depends. Licenses can make things difficult, especially when you are developing closed-source software. Since some OSS licenses even require the employing application to be open-sourced as well (looking at you, GPL), you cannot use such software in a closed-source project.

To be sure on this, we have developed a project-level integration of Pivotal's excellent [license_finder](https:/...

If you have a :string or :text field, you should pair it with a model validation that restricts its length.

There are two motivations for this:

• In modern Rails, database types :string and :text no longer have a relevant size limit. Without a validation a malicious user can quickly exhaust the hard drive of your database server.
• In legacy Rails (or database schemas migrated from legacy Rails), database types :string and :text had a database-side length constraint. When the user enters a longer string, the ActiveRecord valida...

FactoryBot allows to create traits from Enums since version 6.0.0

The automatic definition of traits for Active Record enum attributes is enabled by default, for non-Active Record enums you can use the traits_for_enum method.

Example

factory :user do
  traits_for_enum :role, %w[admin contact] # you can use User::ROLES here, of course
end

is equivalent to

factory :user do
  trait :admin do
    role { 'admin' }
  end

  trait :contact do
    role { 'c...

TL;DR PostgreSQL handles Rails 4+ text and string columns the same. Some libraries may still reflect on the column type and e.g. render differently sized text fields.

PostgreSQL offers three character types for your columns:

• character varying(n) (also called varchar or just string): Contents are limited to n characters, smaller contents are allowed.
• character(n): All contents are padded with spaces to allocate exactly n characters.
• text: There is no upper or lower character limit (except for the absolute...

In a web application you sometimes have tasks that can not be processed during a request but need to go to the background.
There are several gems that help to you do that, like Sidekiq or Resque.

With newer Rails you can also use ActiveJob as interface for a background processing library. See here for a list of supported queueing adapters.
For ...

Select2 comes with AJAX support built in, using jQuery's AJAX methods.
...
For remote data sources only, Select2 does not create a new element until the item has been selected for the first time. This is done for performance reasons. Once an has been created, it will remain in the DOM even if the selection is later changed.

If you have a huge collection of records for your select2 input, you can populate it via AJAX in order to not pollute your HTML with lots of <option> elements.

All you have to do is to provide...

Speaker today is Henning Koch, Head of Development at makandra.

This talk will be in German with English slides.

Introduction

As web developers we work with JavaScript every day, even when our backend code uses another language. While we've become quite adept with JavaScript at a basic level, I think many of us lack a deep understanding of the JavaScript object model and its capabilities.

Some of the questions we will answer in this talk:

• How does the new keyword construct an object?
• What is the differen...

To make CSS rules dependent on the screen size, we use media queries:

@media (max-width: 500px) {
  // rules for screen widths of 500px or smaller
}

Browsers will automatically enable and disable the conditional rules as the screen width changes.

To detect responsive breakpoints from JavaScript, you may use the global matchMedia() function. It is supported in all brow...

In Active Record you can use named bindings in where-conditions. This helps you to make your code more readable and reduces repetitions in the binding list.

Example without named bindings

User.where(
  'name = ? OR email = ?',
  params[:query],
  params[:query]
)

Example with named bindings

User.where(
  'name = :query OR email = :query',
  query: params[:query]
)

With puma you can have concurrent requests. There are two concepts on how Puma can handle two incoming requests: Workers and Threads.

Workers

Puma can have multiple workers. Each worker is a process fork from puma and therefore a very heavy instance and can have multiple threads, that handle the incoming requests.

Example: A Puma server with 2 workers and 1 thread each can handle 2 request in parallel. A third request has to wait until the thread of one of the workers is free.

Threads

Rails is thread-safe since version 4 (n...

A recent patch level Ruby update caused troubles to some of us as applications started to complain about incompatible gem versions. I'll try to explain how the faulty state most likely is achieved and how to fix it.

Theory

When you deploy a new Ruby version with capistrano-opscomplete, it will take care of a few things:

• The new Ruby version is installed
• The Bundler version stated in the Gemfil...

Chrome allows you to throttle the Network and the CPU. Both settings are useful to measure the performance of you application and reproduce performance issues (Example Debugging frontend performance issues with Chrome DevTools).

You find the settings in: DevTools > Performance > Capture Settings (Gear icon in the right corner) > `CPU: No...

We can use ActiveRecord's where to add conditions to a relation. But sometimes our condition is not on the model itself, but on an associated model. This card explains multiple ways to express this condition using ActiveRecord's query interface (without writing SQL).

As an example we will use a User that has many Posts:

class User < ApplicationRecord
  has_many :posts
  scope :active, -> { tra...