3872 cards

Capistrano: Deployment issue undefined method `[]' for nil:NilClass

In newer passenger versions the output of passenger -v has changed. capistrano-passenger tries to parse the version and now causes the error undefined method '[]' for nil:NilClass. To fix this you only need to upgrade the capistrano-passenger gem.

Therefore run bundle update capistrano-passenger.

The version change of passenger from 6.0.7 to 6.0.8 has triggered this problem. This is fixed in capistrano-passenger >= 0.2.1.

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Getting permanent links to files on Github or Gitlab

Please don't simply copy line number links from Github. The URL usually contains a branch name like master which will change over time:


If someone now posts an insertion or deletion to that file into master your link points to the wrong line!

A better way is to press the Y key after clicking on a line number. This will transform the URL to another URL that points to the particular commit:


Copying validation errors from one attribute to another

When using virtual attributes, the attached trait can be useful to automatically copy errors from one attribute to another.

Here is a typical use case where Paperclip creates a virtual attribute :attachment, but there are validations on both :attachment and :attachment_file_name. If the form has a file picker on :attachment, you would like to highlight it with errors from any attribute:

class Note < ActiveRecord::Base
  has_attached_file :attachment
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How to explain SQL statements via ActiveRecord

ActiveRecord offers an explain method similar to using EXPLAIN SQL statements on the database.

However, this approach will explain all queries for the given scope which may include joins or includes.

Output will resemble your database's EXPLAIN style. For example, it looks like this on MySQL:

User.where(id: 1).includes(:articles).explain
EXPLAIN for: SELECT `users`.* FROM `users`  WHERE `users`.`id` = 1
| id | select_type | table | type  | possible_keys |
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The developer console can do more than you think!

You can do so much more than console.log(...)! See the attached link for a great breakdown of what the developer console can give you.

Some of my favorites:

console.log takes many arguments

E.g. console.log("Current string:", string, "Current number:", 12)

Your output can have hyperlinks to Javascript objects

E.g. console.log("Check out the current %o, it's great", location)



Tod: A Gem for handling daytime without a date

Tod is a gem for working with daytimes.

Another additional gem?

Thus SQL has a time datatype for storing time of day in the format hh:mm:ss, neither Ruby nor Rails themselves offer an elegant way to deal with day times.

Time and DateTime both handle daytime values AND calendar date, using them to only store the time of day will end in inconsistent and thus confusing data, e. g. Time.new will initialize with the current Time in your Timezone, DateTime.new initializes at January 1, at an undefined year, without a timezone o...


Git: How to configure git to push only your current branch

You can change which branches will be pushed when saying git push. Our recommendation is to set it to current.

From the git-config documentation:

: ^
Defines the action git push should take if no refspec is given on the command line, no refspec is configured in the remote, and no refspec is implied by any of the options given on the command line. Possible values are:

  • nothing - do not push anything.
  • matching - push all matching branches. All bra...

Deliver Carrierwave attachments to authorized users only


To attach files to your records, you will need a new database column representing the filename of the file. To do this, add a new migration (rails g migration <name>) with the following content:

class AddAttachmentToNotes < ActiveRecord::Migration[6.0]
  def change
    add_column :notes, :attachment, :string

Don't forget to rename the class and change the column details to fit your purpose. Run it.

1) Deliver attachments through Rails


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What does 100% mean in CSS?

The attached article examines what the percent unit (%) is relative to in CSS

The article does a great job of visualizing the dependencies. The TLDR is:

Own property % of
height parent height
width parent width
top parent height
left parent width
margin-top parent width
margin-left parent width
padding-top parent width
padding-left parent width
translate-top own height
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cucumber_factory 1.14 lets you set array fields, has_many associations, numbers without quotes

Setting array columns

When using PostgreSQL array columns, you can set an array attribute to a value with square brackets:

Given there is a movie with the tags ["comedy", "drama" and "action"]

Setting has_many associations

You can set has_many associations by referring to multiple named records in square brackets:

Given there is a movie with the title "Sunshine"
And there is a movie with the title "Limitles...

Why has_many :through associations can return the same record multiple times

An association defined with has_many :through will return the same record multiple times if multiple join models for the same record exist. To prevent this, you need to add ->{ uniq } as second argument to has_many (below Rails 4 it is a simple option: has_many :xyz, :uniq => true).


Say you have an Invoice with multiple Items. Each Item has a Product:

class Invoice < ActiveRecord::Base
  has_many :items
  has_many :products, :through => :items

class Item < ActiveRecord::Base

Using Passenger Standalone for development

For our production servers we use Passenger as a Ruby application server. While it is possible to use Passenger for development as an Apache module, the installation process is not for the faint of heart.

Luckily Passenger also comes as a standalone binary which requires zero configuration.

You can Passenger Standalone as a replacement for Webrick or Thin if you'd like to:

  • Use SSL certificates locally
  • Get performance behavior that is closer to ...

Converting ES6 to ES5 on the command line

I use the TypeScript compiler for this, since its output is more minimal than Babel's.

The following will transpile all src/*.js files into a file build.js:

npm install typescript
npx tsc src/*.js --target ES5 --allowJs --outFile build.js

The output will only transpile ES6 syntax. It will not include any polyfills for missing APIs.

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Updated: Capybara: Execute asynchronous JavaScript

Added a new section introducing an alternative to using evaluate_async_script which seems to work in newer Capybara versions.

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Changes to positional and keyword args in Ruby 3.0

Ruby 3.0 introduced a breaking change in how it treats keyword arguments.

There is an excellent blog post on the official Ruby blog going into the details. You should probably read that, but here is a slightly abbreviated version:

What changed

If you call a method that accepts keyword arguments, either explicitly or via **args, you cannot call it with a hash. I.e.

def explicit_kwargs(x:, y:)
  # ...

def splat_kwar...
Auto-destruct in 40 days

Spreewald 4.1.0 released

New steps:

  • When ... inside the ... iframe

New steps only available for Capybara 3+:

  • When I switch to the ... iframe
  • When I switch back to the whole page

The I switch back to the whole page step does not work reliably with Capybara 2 and lead to StaleReferenceErrors, therefore we decided to not make these steps available for Capybara 2.

Small improvements:

  • Trying to match against unsupported email headers will raise an error. Supported headers are "To", "CC", "BCC", "From", "Reply-To", "Subject", "Attachments"
  • It's ...

RubyMine: How to restore the Back to last position shortcut on Ubuntu 20.04

I really love to use the shortcuts CTRL+Alt+ Arrow Left and CTRL+Alt+ Arrow Right to navigate through the code. It worked great on Ubuntu 18.04 and MATE but after migrating to my new notebook with GNOME and Ubuntu 20.04, I realized that the shortcuts didn't work anymore. Well, it worked via Navigate > Back and also showed the shortcut, but my fingers weren't able to do this...

I cried a lot. (Why God? WHY?)

Then I found this [thread on StackOverflow](https://stackoverflow.com/questions/47808160/intellij-idea-ctrlaltleft-short...

Ruby: How to convert hex color codes to rgb or rgba

When you have a hex color code, you can easily convert it into its RGB values using plain Ruby.

>> "#ff8000".match(/^#(..)(..)(..)$/).captures.map(&:hex)
=> [255, 128, 0]

You can use that to implement a simple "hex to CSS rgba value with given opacity" method:

def hex_color_to_rgba(hex, opacity)
  rgb = hex.match(/^#(..)(..)(..)$/).captures.map(&:hex)
  "rgba(#{rgb.join(", ")}, #{opacity})"
>> hex_color_to_rgba("#ff8000", 0.5)
=> "rgba(255, 128, 0, 0.5)"

If you need to support RGBA hex color codes,...

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