When dealing with time zones in Rails, there is one key fact to keep in mind:

Rails has configurable time zones, while
Ruby is always in the server's time zone

Thus, using Ruby's time API will give you wrong results for different time zones.

"Without" time zones

You can not actually disable time zones, because their existence is a fact. You can, however, tell Rails the only single time zone you'll need is the server's.

config.time_zone = "Berlin" # Local time zone
config.active_record.default_timezone = :loca...

Sometimes you want to write a test for a business rule that's based on multiple variables. In your goal to cover the rule thoroughly, you start writing tests for each permutation of all variables. Quickly it blows up into something unsustainable. With n variables for the business rule, you get 2n permutations/test cases. This is manageable with 2 variables (4 test cases), but at 3 variables (8 test cases) it becomes ridiculous, and anything beyond that feels immediately uncomfortable.

I've noticed myself using an alternate pattern for...

I recently stumbled over a quirk in the way Ruby handles local variables that I find somewhat dangerous.

Consider:

def salutation(first_name, last_name = nil)
  if last_name
    full_name = "#{first_name} #{last_name}"
  end 
  "Hi #{full_name}"
end 

This is obviously wrong, full_name is unset when last_name is nil.

However, Ruby will not raise an exception. Instead, full_name will simply be nil, and salutation('Bob') returns 'Hi '.

The same would happen in an else branch:

def salutation(fi...

Sometimes we have to write code that behaves differently based on the version of a specific gem or the Ruby Version itself. The version comparison can often be seen with simple string comparison like so.

# ❌ Not recommended
if Rails.version > '6.1.7.8' || RUBY_VERSION > '3.1.4'
  raise Error, 'please check if the monkey patch below is still needed'
end

If you are lucky, the version comparison above works by coincidence. But chances are that you are not: For example, Rails version 6.1.10.8 would not raise an error in the code ...

Rails gives you migrations to change your database schema with simple commands like add_column or update.
Unfortunately these commands are simply not expressive enough to handle complex cases.

This card outlines three different techniques you can use to describe nontrivial migrations in Rails / ActiveRecord.

Note that the techniques below should serve you well for tables with many thousand rows. Once your database tables grows to millions of rows, migration performance becomes an iss...

The tree command will show you the contents of a directory and all its sub directories as a tree:

>tree
.
├── a
│   ├── file_1.txt
│   └── file_2.txt
└── b
    ├── c
    │   └── even_more.txt
    └── more.txt

3 directories, 4 files

If you have deeply nested directories, the output will be quite long though. To avoid that, you can limit the depth, e.g. tree -L 2 will only go 2 directories deep.

If you use that regularly, consider adding aliases for that to your ~/.bashrc:

alias tree2='tree -L 2'
alias tree3='tree -L 3'
...

When you're nesting setTimeout(f, 0) calls, your browser will silently increase the delay to 5 milliseconds after the fourth level of nesting.

This is called "timeout clamping" and defined in the HTML spec:

If nesting level is greater than 5, and timeout is less than 4, then set timeout to 4.

Timeouts are clamped harder in background tabs

On a similar note, all major browsers have implemented throttling rules for setInterval and setTimeout calls from tabs...

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...

tl;dr

To adjust code templates in RubyMine, navigate to Settings -> Editor -> File and Code Templates.

Example

You can navigate to the test file of the currently open file with the shortcut Ctrl + T. If no test file exists, you can generate a new test file. If you are not pleased with the output, you can adjust the related code template. To do this, open the project settings and navigate to Editor -> File and Code Templates -> Files. Now, choose your relevant file type and adjust the code template according ...

In Ruby, the meaning of protected and private is different from other languages like Java. (They don't hide methods from inheriting classes.)

private

Private methods can only be called with implicit receiver. As soon as you specify a receiver, let it only be self, your call will be rejected.

class A
  def implicit
    private_method
  end
  
  def explicit
    self.private_method
  end
  
  private
  
  def private_method
    "Private called"
  end
end

A.new.implicit
# => "Private called"

A.new.explicit
# => NoMethod...

If your application exports CSV, be advised that Excel and other spreadsheet applications treat certain cells (those starting with =, +, - or @) as formulas.

This is an issue if you output user input. Not only is it probably not what you want, it also poses a security risk. See the link for attack vectors.

Note that current Excel versions will warn the user when opening the file. At least for the code execution vulnerability, these three warnings seems adequate to me.

Code execution warnings:

![Image](/makandra/47624/attach...

Background

After switching a project from Sprockets to Webpack, I started observing a bug that was hard to debug: Our custom icon font could sometimes not be displayed until a full page reload.

Digging deeper the only difference before and after the page load was the encoding interpretation of the iconfont stylesheet:

Correct representation (UTF-8):

.icon:before {
    content: ""
}

Broken representation (other charset):
`...

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 ...

When Rails releases a new version of their gems, they also release a number of npm packages
like @rails/activestorage or @rails/actioncable.

Unfortunately Rails uses up to 4 digits for their gem version, while npm only allows 3 digits and a pre-release suffix.

To map gem versions and npm versions, Rails is going to use a naming scheme like this:

Modern JavaScript includes Intl.NumberFormat to format numbers in different formats and locales.
In this card, we describe a wrapper for it that humanizes a given number of seconds in the "next best" unit, like seconds, minutes, etc.

Example usage

>> new Duration(42).humanized()
=> '42 Sekunden'
>> new Duration(123456).humanized()
=> '1 Tag'
>> new Duration(123456).humanized('es')
=> '1 día'

Code

Here is the code ...

The Git stash does not work like a one-slot clipboard and you might shoot yourself in the foot if you pretend otherwise.

In particular git stash apply does not remove the stashed changes from the stash. That means you will probably apply the wrong stash when you do git stash apply after a future stashing.

To keep your stash clean, you can use

git stash pop

instead.

Another way to look at it:

git stash pop 

is the same as

git stash apply && git stash drop

Notice: In case of a conflict git will not pop th...

By default parallel_tests will spawn as many test processes as you have CPUs. If you have issues with flaky tests, reducing the number of parallel processes may help.

Important

Flaky test suites can and should be fixed. This card is only relevant if you need to run a flaky test suite that you cannot fix for some reason. If you have no issues...

This card shows an uncommon way to retrieve a file using selenium where JavaScript is used to return a binary data array to Ruby code.

The following code example retrieves a PDF but the approach also works for other file types.

require "selenium-webdriver"

selenium_driver = Selenium::WebDriver.for :chrome
selenium_driver.navigate.to('https://example.com')
link_to_pdf = 'https://blobs.example.com/random-pdf'

binary_data_array = selenium_driver.execute_script(<<-JS, link_to_pdf)
  const response = await fetch(arguments[0])

  if (!r...

See the attached link for a useful overview of modern (and classic) DOM API methods, like matches, contains, append, cssText, etc.

You will still need to look up some documentation, e.g. on how to modify a ClassList, but it's still better than browsing interfaces and superclasses of Element on MDN without knowing what to look for.

When coming from jQuery, also see the card on JavaScript without jQuery. This card includes a link to [You Don't Need jQuery](https://github.com/nefe/You-Dont-Need-jQuery/blob/maste...

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...

If a project ist configured to spawn CI runners for tests or deployment when pushing to the Repo, a habit of pushing WIP commits regularly may conflict with that.
Here are two solutions that allow you to keep pushing whenever you feel like it.

Special commit message

To skip a CI run, simply add [ci skip] or [skip ci] to your commit message. Example:

git commit -m "wip authentication [ci skip]"

Git push options (GitLab)

In addition to that, GitLab CI supports Git push options. Instead of changing your commit message, ...

Some rubygems come in platform-specific versions (i.e. "x86_64-linux") in addition to the usual "ruby" platform. This is often is done for gems with native extensions that want to deliver precompiled binaries for ease of installation. However, there is an issue on some versions of Bundler (at least 2.3.x) that makes it inconsistent which versions of a gem will be installed.

Why this happens

On (very) old versions of Bundler, the Gemfile.lock could never indicate which version of a gem was installed, i.e. the Gemfile read `nokogiri (1....

The nokogiri gem provides different packages for several platforms. Each platform-specific variant ships pre-built binaries of libxml2, e.g. x86_64-linux includes binaries for 64bit Linux on Intel/AMD. This significantly speeds up installation of the gem, as Nokogiri no longer needs to compile libxml2.

However, this also means that for each security issue with libxml2, Nokogiri maintainers have to update their pre-built binaries and release a new version of the gem. Then, you need to update and ...

Chrome's developer tools automagically choose vertical or horizontal panel layout, based on their width. You can disable that magic.

In the developer tools, klick the cogwheel icon (or press F1 when focusing the dev tools) to open the settings overlay.
Under "Preferences", in the "Appearance" section, find the "Panel layout" option. Set it to your liking.

Alternatively, press Ctrl+Shift+P and search for "panel layout".

Wat?

Vertical means that the DOM tree is next to the styles/etc panel, like so:

![vertical layout example](https:/...