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Native app install banners in Android, iOS

You can make both mobile Chrome and mobile Safari display a native app install banner. The banner suggests that the user installs an app that is related to the current page. It is shown in the phone's native UI. See attached animation.

There is some fineprint you need to read to make this work (see below).



Authorize allowed values with assignable_values

All our projects have enum-like requirements like this:

  • An attribute value must be included in a given set of values.
  • The list of allowed values must be retrievable in order to render <select> boxes.
  • Each value has a humanized label.
  • Sometimes there is a default value.

Most of the time, this requirement is also needed:

  • The list of assignable values depends on the user who is currently signed in.

In our past projects there are many different solutions for these related requirements, e.g. ChoiceTrait, methods like `available_…

An auto-mapper for ARIA labels and BEM classes in Cucumber selectors

Spreewald comes with a selector_for helper that matches an English term like the user's profile into a CSS selector. This is useful for steps that refer to a particular section of the page, like the following:

Then I should see "Bruce" within the user's profile

If you're too lazy to manually translate English to a CSS selector by adding a line to features/env/selectors.rb, we already have an [auto-mapper to translate English into …

Matching unicode characters in a Ruby (1.9+) regexp

On Ruby 1.9+, standard ruby character classes like \w, \d will only match 7-Bit ASCII characters:

"foo" =~ /\w+/   # matches "foo"
"füü" =~ /\w+/   # matches "f", ü is not 7-Bit ASCII

There is a collection of character classes that will match unicode characters. From the documentation:

  • /[[:alnum:]]/ Alphabetic and numeric character
  • /[[:alpha:]]/ Alphabetic character
  • /[[:blank:]]/ Space or tab
  • /[[:cntrl:]]/ Control character
  • /[[:digit:]]/ Digit
  • /[[:graph:]]/ Non-blank character (excludes spaces, co…

Preload associations in loaded records

Sometimes you want to fetch associations for an object that you already loaded, e.g. when it has deeply nested associations.

Edge Rider gives your models a static method preload_associations. The method can be used to preload associations for loaded objects like this:

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    User.preload_associations [@user],  { :threads => { :posts => :author }, :messages => :sender }


passenger problems with upgraded rails-app

You may encounter problems with passenger starting an application with an updated rails.
If you find an error like this in the apache error log:

[ 2015-08-21 10:53:04.1266 17680/7f4909bf7700 Pool2/Implementation.cpp:883 ]: Could not spawn process for group /var/www/ An error occured while starting up the preloader.
in 'void Passenger::ApplicationPool2::SmartSpawner::handleErrorResponse(Passenger::ApplicationPool2::SmartSpawner::StartupDetails&)' (SmartSpawner.h:455)
in 'std::string Passenger::Appli…

External content

Continuous Security Testing with Devops - OWASP EU 2014

Interesting talk about a team that integrated automated security testing into their BDD workflow.

There is also a video of the talk.


Gatekeeping: Guide for developer

Note: This has been a private card for some time, because it is heavily tailored to our specific needs and tools. While it will certainly not apply to all (especially larger teams), we thought it might still be helpful as a starting point, and so made it public. Compare also the Gatekeeping: Guide for gatekeeper card.

In order to reduce the number of rejects we get from clients, we want to review all code written before it goes to the staging serv…

Auto-destruct in 58 days

Updated: Rails 4 introduced collection_check_boxes

  • Now showing how the generated HTML and form params looks like.
  • Now showing how to whitelist an array-valued form param in your Rails controller

How Ruby method lookup works

When you call a method on an object, Ruby looks for the implementation of that method. It looks in the following places and uses the first implementation it finds:

  1. Methods from the object's singleton class (an unnamed class that only exists for that object)
  2. Methods from prepended modules (Ruby 2.0+ feature)
  3. Methods from the object's class
  4. Methods from included modules
  5. Methods from the class hierarchy (superclass and its ancestors)


Let's say we …

whenever: Preview the crontab

If you'd like to preview the crontab that whenever will deploy, run the following:

bundle exec whenever

This will print the cron syntax without modifying your local crontab.

postgresql create extension without giving the application superuser rights

If you need a postgresql extension for your database it isn't a good idea to give your applications database user superuser rights (like many people on stackoverflow think)

Just login to the database with a superuser account (e.g. postgres) and create the extension with it.


# with the default configuration of postgresql you normally can login as postgres user
# without a password if you use the systems postgres user
$ sudo su -l postgres
$ pgsql
postgres=# \c your_database;
psql (9.3.9, server 9.3.5)
You are now connected…


Capybara will not find links without an href attribute

Capybara will fail to find <a> tags that are missing an href attribute. This will probably happen to you every now and then on JavaScript-heavy applications.

An example would be an AngularJS application where the following HTML actually works. [1]

<a ng-click="hello()">Hello</a>

Capybara will fail to find that link, even though looking it up via the DOM shows it:

>> find_link("Hello")
Capybara::ElementNotFound: Unable to find link "Hello"

>> find("a").text
=> "Hello"

To make find_link and click_link work…

External content

Flash-Free Clipboard for the Web

Unfortunately, Web APIs haven’t provided the functionality to copy text to the clipboard through JavaScript, which is why visiting GitHub with Flash disabled shows an ugly grey box where the button is supposed to be. Fortunately, we have a solution. The editor APIs provide document.execCommand as an entry point for executing editor commands. The "copy" and cut" commands have previously been disabled for web pages, but with Firefox 41, which is currently in Beta, and slated to move to release in mid-September, it is becoming available to Ja…

External content

AWS Public IP Address Ranges Now Available in JSON Form

I am happy to announce that this information is now available in JSON form at The information in this file is generated from our internal system-of-record and is authoritative. You can expect it to change several times per week and should poll accordingly.


Use find_in_batches to process many records without tearing down the server

Occasionally you need to do something directly on the server – like having all records recalculate something that cannot be done in a migration because it takes a long time.

Let's say you do something like this:


Even though you may have been successful with this on your development machine or the staging server, keep in mind that production machines often hold a lot more records. Using all may just work, even with lots of records, but when you iterate over such records and fetch associati…

Auto-destruct in 47 days

Updated: Matching line feeds with regular expressions works differently in every language

Added a note for Javascript:

You need to write (.|\s) to match any character including line feeds, carriage returns, etc. Note that (.|\n) is not enough.

include_tags with the asset pipeline

You can include files from app/assets or from the public folder with javascript_include_tag. The subtle difference that tells rails how to build the path correctly is a single slash at the beginning of the path:

<%= javascript_include_tag('ckeditor/config') %> # for assets/ckeditor/config.js
<%= javascript_include_tag('/ckeditor/ckeditor') %> # for public/ckeditor/ckeditor.js

This also applies to stylesheet_link_tag.

Note that when you refer to a Javascript or stylesheet in /assets you need to add it to [the list of asse…

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