Rails 5's ApplicationRecord is the place to put generic model logic

Since Rails 5, domain models inherit from ApplicationRecord by default.

This is the place to put code that should be available in all your application's models.
There is no reason to monkey-patch ActiveRecord::Base when following that practice.


How to split up a git commit

Quick steps

  1. git rebase -i -> mark your commit with edit
  2. git reset HEAD~ (remove the marked commit, but keep its changes)
  3. Make several commits
  4. git rebase --continue

Detailed instructions

Basically, you will review the last n commits and stop at the splittable commit. Then you'll undo that commit and put its changes into new commits at your liking.

  1. Review commits (rebase)

    git rebase -i HEAD~3
    # or
    git rebase -i origin/master

    Git will give you a list of commits, younge…


Working with or without time zones in Rails applications

Rails supports time zones, but there are several pitfalls. Most importantly because 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 time…

How to define height of a div as percentage of its variable width

This is useful if, for example, you want to use a background-image that has to scale with the width and the div should only have the height of the picture.


<div class="outer">
  <div class="inner">


.outer {
  width: 100%;
  background-image: image-url('background.png');
  background-size: cover;
.inner {
  padding-top: 60%;

How does it work?

There are several CSS attributes that can handle values as percentage. But they use different other attributes as "reference value…

Listing all gems on a private gem server

You can use gem list to list all gems available from a remote gem server:

gem list -r --clear-sources -s 'https://user:password@gemserver.tld/'

This is useful to debug cases where Bundler complains of a gem existing in more than one gem source.


Understanding race conditions with duplicate unique keys in Rails/MySQL

validates_uniqueness_of is not sufficient to ensure the uniqueness of a value. The reason for this is that in production, multiple worker processes can cause race conditions:

  1. Two concurrent requests try to create a user with the same name (and we want user names to be unique)
  2. The requests are accepted on the server by two worker processes who will now process them in parallel
  3. Both requests scan the users table and see that the name is available
  4. Both requests pass validation and create a user with the seemingly available name…

How to bulk-unwatch many repositories on Github

To easily opt out of notifications for a large number of Github repositories, go to


Minified JavaScript and CSS

JavaScripts and CSS should be minified for production use.

In Rails 3.1+ the asset pipeline will take care of this. Thus you're best off using an uncompressed version of your Javascript in development. Also load the non-minified versions of libraries. This way debugging will be easier and you will still get all the minification love once deployed.

In Rails 2.3 and 3.0 you should at least embed external JavaScript libraries in minified form, using something like JavaScript compressor.

Ubuntu: keyring password won't change with user password

Ubuntu might create several keyrings for you. Note that keyring passwords are initially set to the user password but do not change with it. If you can't seem to find the correct password for a keyring, try entering the inital password.

If you still can't find it, you might have to delete that keyring:

  • open "Passwords and Keys" (seahorse application)
  • make sure, View > By keyring is checked
  • right-click on the keyring you want to change
  • press Delete

Git: rebase dependent feature branch after squash

This card will show you how to use git rebase --onto without confusion.

Use case:

You've got two feature branches (one and two), where two depends on one. After code review the commits of branch one are squashed. Thus the commit history this branch has changed. Branch two however didn't change. To make the branches share the same commit history again you will have to rebase and replay the additional commits of branch two onto branch one.


The easiest way for me to correctly use `git rebase –o…


Webmock normalizes arrays in urls

Typhoeus has a different way of representing array params in a get request than RestClient.


Webmock normalizes this url when matching to your stubs, so it is always[]=1&foo[]=2&foo[]=3. This might lead to green tests, but in fact crashes in real world. Rack::Utils.build_nested_query might help to build a get re…


How to use the Capistrano shell to execute commands on servers

Capistrano brings the shell command which allows you to run commands on your deployment targets.
There is also invoke to run a command directly from your terminal.

Both commands allow running Capistrano tasks or shell commands, and scope to individual machines or machine roles.

cap shell


First of all, spawn a Capistrano shell (we're using the multistage extension here):

$ cap staging shell

In your "cap" shell you can now run Capistrano tasks by prepending an exclamation mark. For example:

cap> !deploy:revisi...

Escape a string for transportation in a URL

To safely transport an arbitrary string within a URL, you need to percent-encode characters that have a particular meaning in URLs, like & or =.

If you are using Rails URL helpers like movies_path(:query => ARBITRARY_STRING_HERE), Rails will take care of the encoding for you. If you are building URLs manually, you need to follow this guide.


In Ruby, use CGI.escape:

=> "foo%3Dfoo%26bar%3Dbar"

Do not ever use URI.encode or …

Capistrano 2: How to deploy a single server

When you have a multi-server setup, you'll be adding a new server from time to time. Before doing a full deploy, you might want to test that server in an isolated deploy. There is a single way to do this: the HOSTFILTER env variable.

Commenting out "server" lines in the Capistrano deploy config will raise a Capistrano::NoMatchingServersError with <task> is only run for servers matching {:roles=> <role>}, but no servers matched. Instead, specify the server-under-test like this:

``` cap productio…

Testing webpages globally (as in "around the globe")

These tools help you in checking websites globally:

DNS Checker
This tool allows for global DNS propagation checking.
This tool takes screenshots of a given URL from various locations across the world.

Webmock's hash_including doesn't parse query values to string

Webmocks hash_including is similar to RSpec::Mocks::ArgumentMatchers#hash_including. Be aware that hash_including (webmock v3.0.1) doesn't parse integer values to String.

Without hash including you would say:

uri = URI('')
stub_request(:get, '').with(query: {foo: 1, bar: 2})
Net::HTTP.get(uri) # ===> Success

If you only want to check if foo is present you can use hash_including:

uri = URI('')
stub_request(:get, '').with(query: hash_i…


Use Time.current / Date.current / DateTime.current on projects that have a time zone

This ancient card is no longer entirely correct for newer Railses and was rewritten.

Basically, you now need to know if your project uses a "real" time zone or :local, and if config.active_record.time_zone_aware_attributes is set to false or not.

  • With time zones configured, always use .current for Time, Date, and DateTime.

    ActiveRecord attributes will be time-zoned, and .current values will be converted properly when written to the database.
    Do not use and friends. Timezone-less objects will not be convert…

External content

Standard Gems

Ruby's standard library is in the process of being gemified. It will soon - Ruby 2.5 - consist of RubyGems, which can be updated independently from Ruby.

This might mean smoother Ruby upgrades in the future. If breaking API changes happen in standard gems, we can update these before upgrading Ruby.

3404 cards