How to mount a legacy database to migrate data

There are many approaches out there how you can import data from a legacy application to a new application. Here is an approach which opens two database connections and uses active record for the legacy system, too:

1. Add you database information to you config/database.yml.

  database: your_application_data_migration

2. Create a separate application record for the data migration, e.g. in app/data_migration/migration_record.rb. You will need to create an app/data_migration.rb class first.

class DataMig…


How to solve Selenium focus issues

Selenium cannot reliably control a browser when its window is not in focus, or when you accidentally interact with the browser frame. This will result in flickering tests, which are "randomly" red and green. In fact, this behavior is not random at all and completely depends on whether or not the browser window had focus at the time.

This card will give you a better understanding of Selenium focus issues, and what you can do to get your test suite stable again.

Preventing accidental interaction with the Selenium window ——————–…

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How to: Use git bisect to find bugs and regressions

Git allows you to do a binary search across commits to hunt down the commit that introduced a bug.

Given you are currently on your branch's HEAD that is not working as expected, an example workflow could be:

git bisect start # Start bisecting
git bisect bad # Tag the revision you are currently on (HEAD) as bad. You could also pass a commit's SHA1 like below:
git bisect good abcdef12345678 # Give the SHA1 of any commit that was working as it should
# shorthand:
git bisect start <bad ref> <good ref>

Git will fetch a comm…

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Faking and testing the network with WebMock

An alternative to this technique is using VCR. VCR allows you to record and replay real HTTP responses, saving you the effort to stub out request/response cycles in close details. If your tests do require close inspection of requests and responses, Webmock is still the way.

WebMock is an alternative to FakeWeb when testing code that uses the network. You sh…


Rails: Do not load frameworks you don't need

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…

Known MariaDB version incompatibilities

MariaDB (and MySQL) is released in different versions with different behaviors. For backwards compatibility this can be managed with the sql_mode option.

Following you can find behavior differences which cannot be changed by this option. This can cause a regression in an existing application. There is no workaround available. The application needs to be adapted.

Queries with aggregated date types

For a database instance of MariaDB-10…

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Casting ActiveRecord scopes or instances to ActiveType extended model classes

When working with ActiveType you will often find it useful to cast an ActiveRecord instance to its extended ActiveType::Record variant.

Starting with active_type 0.4.0 you can use ActiveType.cast for this:

class User < ActiveRecord::Base

class SignUp < ActiveType::Record[User]

user = User.find(1)
sign_up = ActiveType.cast(user, SignUp)
sign_up.is_a?(SignUp) # => true

This is basically like [ActiveRecord#becomes](…


Dealing with I18n::InvalidPluralizationData errors

When localizing model attributes via I18n you may run into errors like this:

I18n::InvalidPluralizationData: translation data { ... } can not be used with :count => 1. key 'one' is missing.

They seem to appear out of the blue and the error message is more confusing than helpful.

TL;DR A model (e.g. Post) is lacking an attribute (e.g. thread) translation.
Fix it by adding a translation for that model's attribute ( The error message reveals the (wrongly) located I18n data (from attributes.thread)….

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Write custom RSpec matchers

There are three ways to define your own RSpec matchers, with increasing complexibility and options:

1) Use RSpec::Matchers.define

RSpec::Matchers.define :be_a_multiple_of do |expected|
  match do |actual|
    actual % expected == 0
  # optional
  failure_message do |actual|
    "expected that #{actual} would be a multiple of #{expected}"
  # optional
  failure_message_when_negated do |actual|
    "expected that #{actual} would not be a multiple of #{expected}"

This is automat…


Ruby: How to use global variables for a conditional debugger

You can share a state in Ruby with global variables. Even if you should avoid them whenever possible, for debugging an application this could be temporary quite handy.


class User

  after_save { byebug if $debug; nil }

  def lock
   self.locked = true


Rspec.describe User do

let(:user) { create(:user) }

before do
# Many users are created and saved in this hook, but we don't want the debugger to stop for them
end …


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

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 converted properly when written to the database.

  • With no/local time zone use, `…

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Choosing the right gems for your project

Adding a gem means you take over the liability towards the external code.


Based on "To gem, or not to gem":

  • Gem is really needed (prefer writing your own code for simple requirements without many edge cases)
  • Gem is tested well (coverage and quality)
  • Gem has a good code quality
  • Gem's licence fits to the project requirement
  • Try to avoid gems that do much more than your requireme…

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…


RubyMine: Efficiently filtering results in the "Finder" overlay

RubyMine comes with a nice way to grep through your project's files: The finder (ctrl + shift + f). Don't be discouraged about the notice 100+ matches in n+ files if your searched keyword is too general or widely used in your project.


RubyMine comes with a few ways to narrow down the resulting list, don't hesitate to apply those filters to speed up your search. Your keybinding might vary based on your personal settings.

File mask (alt + k)

If you already know the file extension of your …


Browsers will not send a referrer when linking from HTTPS to HTTP

  • When your site is on HTTPS and you are linking or redirecting to a HTTP site, the browser will not send a referrer.
  • This means the target site will see your traffic as "direct traffic", i.e. they cannot distinguish such hits from a user who directly typed in the URL.

Reasons for this behavior

It's probably because of this RFC:

Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferr…


Jasmine: using async/await to write nice asynchronous specs

Jasmine has long standing support for writing asynchronous specs. In days gone by we used the done callback to achieve this, but these days it is possible to write much more readable specs.

Async specs

As a first example, say we want to check that some form disables the submit button while working.

// bad (how we used to do it)

beforeEach(() => {
this.form = setupMyForm()
this.submitButton = findTheSubmitButton()

it('disables the submit button while working', (done) => {
expect(this.submitButton.disabled).toBe(false) …


ActiveType 1.2 supports "change_association"

With ActiveType 1.2 you can modify associations (has_many etc.) after they have been defined.

One common use case for this is to change an association inside a form model, like this:

class Credential < ActiveRecord::Base

class User < ActiveRecord::Base
  has_many :credentials

class SignUpCredential < ActiveType::Record[Credential]

class SignUp < ActiveType::Record[User]
  change_association :credentials, class_name: 'SignUpCredential'

Now, if you load credentials, y…

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Active Record and PostgreSQL — Ruby on Rails Guides

Rails guide that covers PostgreSQL-specific column types and usages for Active Record.

You should especially keep in mind the special datatypes that PostgreSQL offers. \
Types like json and array take away a lot of the pain that you had on MySQL projects.

Example use cases for array are tags or storing foreign keys (instead of a join model). You can even index them.

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