Also see the list of IRB commands.

Switching the context

Changes the "default receiver" of expressions. Can be used to simulate a "debugger situation" where you are "inside" an object. This is especially handy when needing to call private methods – just invoke them, no need to use send.

• Switch to an object: chws $object
• Reset to main: chws
• Show current context: cwws (usually shown in IRB prompt)

[Technical details](https://technology.doximity.com/articles/the-hidden-gems-of-r...

In development, we store files using ActiveStorage's disk service. This means that stored files are served by your Rails application, and every request to a file results in (at least!) one non-trivial log entry which can be annoying. Here is how to disable those log entries.

Example

Here is an example of what loading a single <img> in an example application writes to the Rails log.

Started GET "/rails/active_storage/blobs/redirect/..." for ::1 at ...
Processing by ActiveStorage::Blobs::RedirectController#show as SVG
  Parameter...

Some key highlights and points from the linked article TestProf II: Factory therapy for your Ruby tests.

The Problem with Factories in Ruby Tests

• Factories are used to easily generate test data.
• However, they can unintentionally slow down test suites by creating unnecessary or excessive associated data (factory cascades).

Understanding Factory-Induced Slowdowns

• Factories often create additional data (e.g., associated records) th...

A lesser known fact about PG enums is that they are ordered. This can be really handy when values have an implicit ordering.

Let's imagine a record Issue(criticality: string). criticality should have the following three possible values: critical, medium, low.

Sorting with Issue.all.order(criticality: :desc) will return the following order:

1. The 'medium' issue
2. The 'low' issue
3. The 'critical' issue

This happens because the database column backing the criticality attribute is a string and PG will use a [collation](...

We recently migrated a Rails application from yarn to npm. We decided to go this step instead of upgrading to > Yarn 2.0 to reduce the number of dependencies in our project.

Migration

• Remove the yarn.lock file
• Remove the node_modules folder
• Run npm install
• Replace all occurrences of yarn with npm in your project

Notes

• With npm vendored packages with dependencies create their own node_modules folder within the vendor path. We...

Slow test suites are a major pain point in projects, often due to RSpec and FactoryBot. Although minitest and fixtures are sometimes viewed as outdated, they can greatly improve test speed.

We adopted a project using minitest and fixtures, and while it required some initial refactoring and establishing good practices, the faster test suite was well worth it! Stick with me to explore how these tools might actually be a good practice.

So, why is this setup faster? Partially, it's because minitest is more lightweight than RSpec, which...

While the main goal always is to prevent long-running queries in the first place, automatic timeouts can serve as a safety net to terminate problematic queries automatically if a set time limit is exceeded. This prevents single queries from taking up all of your database’s resources and reduces the need for manual intervention that might destabilize or even crash the application.

As Rails does not set a timeout on database statements by default, the following query will run for an entire day:

ActiveRecord::Base.connection.execute("S...

On our Ubuntu machines we have nautilus file manager with nautilus-extension-gnome-terminal installed. This adds an entry to the context menu (right click) to start a gnome-terminal in the current directory. As I'm mostly using Terminator terminal, I wanted to have a similar context menu entry to launch Terminator directly. I came across this python script that does exactly that.

• Install python3-nautilus: sudo apt install python3-nautilus
• Create `/usr/share/nautilus-...

Starting with ChromeDriver 127, if your application displays a beforeunload confirmation dialog, ChromeDriver will immediately close it. In consequence, any automated tests which try to interact with unload prompts will fail.

This is because ChromeDriver now follows the W3C WebDriver spec which states that any unload prompts should be closed automatically.
However, this applies only to "HTTP" test sessions, i.e. what you're using by default. The spec also defines that bi-directional test se...

I recently stumbled upon the Rails feature composed_of. One of our applications dealt with a lot of addresses and they were implemented as 7 separate columns in the DB and Rails models. This seemed like a perfect use case to try out this feature.

TLDR

The feature is still a VERY leaky abstraction. I ran into a lot of ugly edge cases.

It also doesn't solve the question of UI. We like to use simple_form. It's currently not possible to simply write `f...

You can improve your LIKE / ILIKE search queries in PostgreSQL by adding a GIN index with an operate class ("opclass") to split the words into trigrams to the required columns.

Example

class AddSearchTextIndexToUsers < ActiveRecord::Migration[7.1]
  def change
    enable_extension 'pg_trgm'

    add_index :users, :search_tex...

Recently I needed to benchmark an Active Record query for performance measurements. I wrote a small script that runs each query to benchmark 100 times and calculates the 95th percentile.

Note: The script requires sudo permissions to drop RAM cache of PostgreSQL. Due to the number of iterations it was impractical to enter my user password that often. And I temporary edited my /etc/sudoers to not ask for the sudo password with johndoe ALL=(ALL) NOPASSWD: ALL.

# Run this script with e.g. `rails ru...

testing-library are widely used testing utilities libraries for javascript dependent frontend testing. The main utilities provided are query methods, user interactions, dom expectations and interacting with components of several frontend frameworks, which allows us to worry less about the details happening in the browser and focus more on user centric tests instead!

Some of the time you will find a necessity to use methods like [waitFor](https://testing-library.com/docs/dom-testing-library/api-async/...

You are given two CSS selectors that you do not control. How can you build a new selector that matches both of them?

item_selector = 'div'
active_selector = '.is-active'

Can't I just concat these selectors?

# Bad
new_selector = "#{item_selector}#{active_selector}"
# => "div.is-active"

Don't! This will break as soon as one of the selectors is actually a selector list.

item_selector = 'div, span, p' # <- Selector list 
new_selector # => "div, span, p.is-active" (wrong)

Solution

Wrap both selectors ...

Reacting on a class getting added can be done with a mutation observer. Example:

const items = document.querySelectorAll('.item')
const expectedClass = 'active'
const activeObserver = new MutationObserver((mutations) => {
  mutations.forEach((mutation) => {
    if (mutation.target.classList.contains(expectedClass) {
      // Do something
    }
  })
})
items.forEach(item => activeObserver.observe(item, { attributes: true, attributeFilter: ['class'] }))

Note that this is not a generic solution – it makes a few assumptions to simplif...

I was recently asked to optimize the response time of a notoriously slow JSON API endpoint that was backed by a Rails application.
While every existing app will have different performance bottlenecks and optimizing them is a rabbit hole of arbitrary depth, I'd like to demonstrate a few techniques which could help reaching actual improvements.

The baseline

The data flow examined in this card are based on an example barebone rails app, which can be used to reproduce the r...

While most Rails Apps are tied to at least one external REST API, machine-to-machine communication via GraphQL is less commonly seen. In this card, I'd like to give a quick intro on how to query a given GraphQL API - without adding any additional library to your existing app.

Core aspects of GraphQL

Interacting with GraphQL feels a bit like querying a local database. You are submitting queries to fetch data in a given structure (like SELECT in SQL) or mutations to alter the database (similar to POST/PUT/DELETE in REST). You can ...

Debouncing a method call delays its execution until after a specified time has passed.
If it's called again before that time has passed, its execution is delayed again.

This technique is commonly used to improve performance when code would be run more often than it needs to.
One example for that are scroll event handlers in JavaScript: You want to react to a user scrolling, but it's enough to do that when they have stopped scrolling.

Here is a small JavaScript function that you can use for that:

function debounce(callback...

This card is a short summary on different ways of assigning multiple attributes to an instance of a class.

Using positional parameters

Using parameters is the default when assigning attributes. It works good for a small number of attributes, but becomes more difficult to read when using multiple attributes.

Example:

class User
  def initialize(salutation, first_name, last_name, street_and_number, zip_code, city, phone_number, email, newsletter)
    @salutation = salutation
    @first_name = first_name
    @last_name = last_nam...

Using Capistrano, we usually have some array configurations in the config/deploy.rb file, like set :linked_files, %w[config/database.yml], so in this case we don't have to manage the database configuration individually on every server.

In a specific case, one of our projects supports sign in by SAML, but not every deploy target has this feature activated. Here comes a nice handy Capistrano feature, which lets us modify the default configuration for individual env...

ActiveModel classes have a class method .human_attribute_name. This returns a human-readable form of the attribute:

Person.human_attribute_name(:first_name) # => "First name"

By default Rails will use String#humanize to format the attribute name, e.g. by replacing underscores with spaces and capitalizing the first word. You can configure different translation in your I18n locales, e.g. in config/locales/en.yml:

en:
  activerecord:
    attributes...

I used two lab days to read the The framework field guide - Fundamentals, the first of a three part series to learn the basics of frontend technologies. I can highly suggest it for learning the fundamentals. 'The framework field guide' is written by Unicron Utterances and there side has many high quality articles on web development and computer science related to programming.

[The Framework Field Guide](https://unicorn-ut...

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...

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...