Working with a self-signed certificate is much easier, when the browser accepts it.

Google Chrome

Warnings from chrome might not be accurate

Even though the certificate is working locally, chrome might still complain that the certificate is not valid and the connection is not secure while blotting out the "https" part of the url.

Accept a specific certificate

• Go to chrome://settings/certificates
• Under "Authorities", click "Import"
• Select the certificate file (.crt)
• Check "Trust this certificate for identi...

Within an event handler, there are multiple methods to cancel event propagation, each with different semantics.

• event.preventDefault()

  Only prevents the default browser behavior for the click, i.e. going to a different url or submitting a form.

  When invoked on a touchstart event, this also prevents mouse events like click to be triggered.

• event.stopPropagation()

  Prevents the event from bubbling up the DOM.

• `event.st...

Rails supports time zones, but there are several pitfalls. Most importantly because Time.now and Time.current are completely different things and code from gems might use one or the other.

Especially configuring an application that cares only about one time zone is a bit tricky.

The following was tested on Rails 5.1 but should apply to Rails 4.2 as well.

Using only local time

Your life will be easier if your application does not need to support time zones. Disable them like this:

config.time_zone = 'Berlin' # Your local ...

Sometimes the need arises for SSL in local development. We have guides for different webservers, this one is for puma.

0. make sure mkcert is installed

1. create an SSL certificate for localhost with mkcert:

$ mkcert-v1.4.4-linux-amd64 localhost
Created a new local CA 💥
...

2. use the certificate in the Puma config config/puma.rb:

localhost_key = "#{File.join('localhos...

Note

Use yarn dedupe in Yarn v2+: https://yarnpkg.com/cli/dedupe

This package only works with Yarn v1. Yarn v2 supports package deduplication natively!

A duplicate package is when two dependencies are resolved to a different version, even when a single version matches the range specified in the dependencies. See the Deduplication strategies section for a few examples.

Yarn is stupid, so it can happen that there are several version of the same package in your bundle, although one would fulf...

Rails is split into a large number of (sub-) frameworks.

The most important and central of those are

• activesupport (extends the Ruby standard library)
• activerecord / activemodel (ORM for Rails)
• actionview / actionpack (controller / views)
• actionmailer (sends mails)

However, there are also some more situational frameworks included, such as

• actioncable (real time communications using websockets)
• actionmailbox (receives mails)
• actiontext (support for WYSIWYG text editor)
• activejob (background jobs)
• activestorage (file uplo...

tl;dr

The :is() pseudo selector - specificity of its most specific argument - matches against a comma-separated list of selectors.

Example

Compound selectors like ...

.datepicker .prev, .datepicker .next, .datepicker .switch
  padding-bottom: 1rem

ul li, ol li
  list-style-type: none

can be simplified by using the :is() pseudo selector ...

.datepicker :is(.prev, .next, .switch)
  padding-bottom: 1rem

:is(ul, ol) li
  list-style-type: none

Hint

The specificity of :is() is equals t...

tl;dr

The :where() pseudo selector - zero specificity - matches against a comma-separated list of selectors.

Example

Compound selectors like ...

.datepicker .prev, .datepicker .next, .datepicker .switch
  padding-bottom: 1rem

ul li, ol li
  list-style-type: none

can be simplified by using the :where() pseudo selector ...

.datepicker :where(.prev, .next, .switch)
  padding-bottom: 1rem

:where(ul, ol) li
  list-style-type: none

Hint

The specificity of :where() is always zero!

I...

Don't sum up columns with + in a sql-query if NULL-Values can be present.

MySQL and PostgreSQL cannot sum up NULL values with the + value. The sum value will be NULL.

MySQL:

mysql> select 1 + 2 + 3;
+-----------+
| 1 + 2 + 3 |
+-----------+
|         6 |
+-----------+
1 row in set (0,00 sec)

mysql> select 1 + NULL + 3;
+--------------+
| 1 + NULL + 3 |
+--------------+
|         NULL |
+--------------+
1 row in set (0,00 sec)

Postgres:

test_database=# select 1 + 2 + 3;

 ?column? 
----------
        6
(1 row)

t...

If you want to have an English Ubuntu UI, but still see dates, money amounts, paper formats, etc. in German formats, you can fine-tune your /etc/default/locale like this:

LANG="en_US.UTF-8"
LC_CTYPE="de_DE.UTF-8"
LC_NUMERIC="de_DE.UTF-8"
LC_TIME="de_DE.UTF-8"
LC_COLLATE="de_DE.UTF-8"
LC_MONETARY="de_DE.UTF-8"
LC_PAPER="de_DE.UTF-8"
LC_NAME="de_DE.UTF-8"
LC_ADDRESS="de_DE.UTF-8"
LC_TELEPHONE="de_DE.UTF-8"
LC_MEASUREMENT="de_DE.UTF-8"
LC_IDENTIFICATION="de_DE.UTF-8"

Make sure you have both en...

If validations failed for a record, and you want to find out if a specific validation failed, you can leverage ActiveModel's error objects.
You rarely need this in application code (you usually just want to print error messages), but it can be useful when writing tests.

As an example, consider the following model which uses two validations on the email attribute.

class User < ApplicationRecord
  validates :email, presence: true, uniqueness: true
end

Accessing errors

Let's assume we have a blank user:

user = Us...

When your Rails application offers downloading a bunch of files as ZIP archive, you basically have two options:

1. Write a ZIP file to disk and send it as a download to the user.
2. Generate a ZIP archive on the fly while streaming it in chunks to the user.

This card is about option 2, and it is actually fairly easy to set up.

We are using this to generate ZIP archives with lots of files (500k+) on the fly, and it works like a charm.

Why stream downloads?

Offering downloads of large archives can be cumbersome:

• It takes time to b...

Recently we detected a memory leak in one of our applications. Hunting it down, we found that the memory leak was located in Rails' #prepend_view_path. It occurs when the instance method prepend_view_path is called in each request, which is a common thing in a multi-tenant application.

On top of leaking memory, it also causes a performance hit, since templates rendered using the prepended view path will not be cached and compiled anew on each request.

This is not a new memory leak. It was [first reported in in 2014](https://github.com/...

Note

The maintenance mode is enabled on all application server as soon as the file /public/system/maintenance.html is present.

Installation

Add this line to your application's Gemfile:

 gem 'capistrano', '~> 3.0'
 gem 'capistrano-maintenance', '~> 1.0'

Add this line to you application's Capfile:

require 'capistrano/maintenance'

Enable task

Present a maintenance page to visitors. Disables your application's web interface by writing a #{maintenance_basename}.html file to each web server. The servers m...

Around will not happen until after a feature's Background has been processed. Use Before and After to avoid that.

Details

Consider this Cucumber feature file:

Feature: Something that needs to be tested

  Background:
    Given a user
      And I sign in        
    
  Scenario: Sign out
    When I sign out
    Then I should see "Signed out"
  
  Scenario: Something else
    # ...

Now, assume you have these step definitions:

Around do
  puts "** Around: before yield"

...

In the DevTools settings, there's a "Shortcuts" section. Found these keyboard shortcuts there:

General

ESC

Toggle drawer

CTRL + ~ or CTRL + `

Show console in drawer

Styles

SHIFT + up/down

Change number by 10

CTRL + up/down

Change number by 100

Elements

H

Toggle "visibility:hidden!important" (useful when debugging page repaint times)

CTRL + hover above element in the DOM list

Don't show the yellow dimensions tooltip (useful when the tooltip covers just the area you need to see).

Drag...

The linked content includes a few design patterns implemented with Ruby on Rails.

What is the card indented to achieve?

• You can use the pattern names for code reviews, so all parties know with only a few words which change is requested. Example: "Please use a form object here"
• You can learn about new code patterns
• You should read the sections "Advantages of using design patterns" and "Disadvantages of using design patterns in a wrong way", since design patterns do not replace good code

Included Design Patterns: Service, Value objec...

These are the results of the "personal tech stack survey". I've included only the most popular mentions, maybe it can help you find one or two useful tools for your own usage.

Desktop environment

pie title Desktop environment
    "Gnome" : 16
    "i3": 2
    "sway": 2
    "awesome": 1
    "bspwm": 1
    "mate": 1
    "xfce": 1

Gnome dominates (unsuprising, it's the Ubuntu default), but quite a few people use tiling window managers, most popular i3 and the mostly i3-compatible [sway](https://swaywm....

This should be fixed in the latest LTS-branches of our mysql2 fork, 0.2.x-lts and 0.3.x-lts.

Use

gem 'mysql2', git: 'https://github.com/makandra/mysql2', branch: '0.2.x-lts' # for Rails 2.x
gem 'mysql2', git: 'https://github.com/makandra/mysql2', branch: '0.3.x-lts' # for Rails 3.x

in your Gemfile, and do a

bundle update mysql2

Background

mysql2 used to check that the client library used at runtime actually matches the one it was compiled against. However, at least on Ubunt...

To read the Rails session from a Rack middleware, use env['rack.session']. It's an ActionDispatch::Request::Session object.

class MyMiddlware

  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, body = @app.call(env)
    session = env['rack.session']
    Rails.logger.info("Value of session['foo'] is: " + session['foo'].inspect)
    [status, headers, body]
  end

end

You may not be able to write to the session this way (I haven't tested this).

An end-to-end test (E2E test) is a script that remote-controls a web browser with tools like Selenium WebDriver. This card shows basic techniques for fixing a flaky E2E test suite that sometimes passes and sometimes fails.

Although many examples in this card use Ruby, Cucumber and Selenium, the techniques are applicable to all languages and testing tools.

Why tests are flaky

Your tests probably look like this:

When I click on A
And I click on B
And I click on C
Then I should see effects of C

A test like this works fine...

Sometimes you want git to ignore certain files that appear on your machine. You can do this in 3 ways:

• Per project, in the project's .gitignore file
• Per project, in a local exclude file
• Globally on your machine

Downsides of per-project .gitignore entries

While it might be tempting to set it per project (other devs might benefit from it), you

• need to do it each time for every project
• "pollute" a project's .gitignore file with stuff...