By default most exceptions in Rails will render a 500 error page and will create a new issue in your error monitoring. There are some built-in rules in Rails that

• render a different error than 500
• will rescue the exception and not create an issue in your error monitoring

A good example is ActiveRecord::NotFound: You don't want an exception in your error monitoring when users navigate to e.g. a blog post t...

The pitfall

Rails Active Support provides some helpful methods for calculating times and dates, like Duration#ago or Duration#from_now. But beware when using those, because they wont give you Dates or Times but ActiveSupport::TimeWithZone instances. As the class name hints, you now have to be awa...

Rails offers the fresh_when method to automatically compute an ETag from the given record, array of records or scope of records:

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    fresh_when @user
  end  
  
  
  def index
    @users = User.all.to_a
    fresh_when @users
  end
end

When your view also displays other records (typically associations), those other records should be included in the ETag. You can do so by passing an array of ETaggable objects to fresh_when.

...

By activating strict_loading you force developers to address n+1 queries by preloading all associations used in the index view. Using an association that is not preloaded will raise an ActiveRecord::StrictLoadingViolationError.

I think it's a good default to activate strict_loading in your controllers' #index actions. This way, when a change introduces an n+1 query, you...

Testing your responses in Rails allows to parse the body depending on the response MIME type with parsed_body.

get '/posts.json'
response.parsed_body # => [{'id' => 42,  'title' => 'Title'}, ...]

For JSON APIs we often parse the response as symbolized keys with JSON.parse(response.body, symbolize_names: true), which is not supported by parsed_body. For all other cases you might want to drop JSON.parse(response.body) and replace it w...

We will achieve this by creating a block accepting method to optionally create and then lock a .lock File of the underlying accessed file.

Why create a .lock file?

• The main advantage of creating a .lock file is that #flock might block some operations and require the index node of the file to be consistent. Some operations might change that index node.
• In some cases it might also be convenient to just read/write the lock file first and update the other file afterwards or vice versa, such that breaking of a process does not...

The change_column method for rails migrations support casting with a custom SQL statement. This allows us to change a column type and keep the former content as the new type. This way, we can for example prepare an address number column to hold German address numbers, which can contain letters:

Example (in most cases not a good idea!)

class ChangeAnIntegerColumnToString < ActiveRecord::Migration[6.1]
  def up
    change_column :users, :address_number, 'varchar USING CAST(rating AS varchar)'
  end

  def down
    change_column ...

Container queries enable you to apply styles to an element based on the size of the element's container. If, for example, a container has less space available in the surrounding context, you can hide certain elements or use smaller fonts. Container queries are an alternative to media queries, which apply styles to elements based on viewport size or other device characteristics.

This feature is now stable across browsers.

Warning

This feature landed in browsers in the beginning of 2023. According to our support policy this will bec...

If you need a sample video with certain properties for a test you can create one using ffmpeg.
You might want a very low bitrate file to speed up processing in your test. (e.g. you only care about the length, then you can create a video with a very low resolution and framerate)

Create a 21s video with 1fps and 10x10 resolution:
ffmpeg -t 21 -s 10x10 -r 1 -f rawvideo -pix_fmt rgb24 -i /dev/zero sample_21_seconds.mp4

This is a checklist I use to work on issues. For this purpose I extracted several cards related to the makandra process and ported them into a check list and refined that over time a little bit.

This task list is divided by the Gate keeping process in the following steps:

1. Starting a new feature
2. Working on the issue
3. Finishing a feature
4. After Review

Here are some ti...

Rails partials have a lot of "hidden" features and this card describes some non-obvious usages of Rails Partials.

Rendering a basic partial

The most basic way to render a partial:

render partial: 'partial' 

This will render a _partial.html.erb file. Notice how all partials need to be prefixed with _.

It's possible to define local variables that are only defined in the partial template.

# _weather.html.erb
<h1>The weather is <%= condition %></h1>

# index.html.erb
render partial: 'weather', locals: { condition: ...

Not all email clients support external images in all situations, e.g. an image within a link. In some cases, a viable workaround is to turn your images into inline attachments.

Note

Rails provides a simple mechanism to achieve this:

• https://guides.rubyonrails.org/action_mailer_basics.html#making-inline-attachments

This documentation makes it look like you have to care about these attachments in two places. You have to create the attachment in t...

Carrierwave's BaseUploader can have some validations that you can use by overriding a certain method, which's expected name is hard coded. A popular example is extension_allowlist, which returns an array of strings and let's you only upload files that have a filename with an extension that matches an entry in that array. Another useful validation can be size_range, which gives you a little bit of control over how your storage gets polluted.

This is often good enough, but some times you need to validate special cases.

Validations t...

Since Rails 7 you are able to encrypt database information with Active Record. Using Active Record Encryption will store an attribute as string in the database. And uses JSON for serializing the encrypted attribute.

Example:

• p: Payload
• h: Headers
• iv: Initialization Vector
• at: Authentication Tag

{ "p": "n7J0/ol+a7DRMeaE", "h": { "iv": "DXZMDWUKfp3bg/Yu", "at": "X1/YjMHbHD4talgF9dt61A=="} }

Note this before encrypting attributes with Active Record:
...

Sometimes I ran across a GitHub merge request of a gem where it was not completely obvious in which version the change was released. This might be the case for a bugfix PR that you want to add to your project.

Git can help you to find the next git tag that was set in the branch. This usually has the name of the version in it (as the rake release task automatically creates a git tag during release).

git name-rev --tags <commit ref>

Note

The more commonly used git describe command will return the last tag before a c...

• To retrieve only unique combinations of the selected attributes: You can omit rows, where all selected columns are equal with the DISTINCT statement.
• To retrieve the group wise maximum of certain columns: You can keep only one record for each group with the DISTINCT ON statement, to omit equal rows within each specified group.

Use case

You have a query where you want only one record for a set of specifically ordered attributes.

How to use?

Let's say we look at the example how to query only the latest post for each user:
...

Rails includes milliseconds in Time / DateTime objects when rendering them as JSON:

JSON.parse(User.last.to_json)['created_at']
#=> "2001-01-01T00:00:00.000+00:00"

In RSpec you might want to use .to_json instead of .iso8601 to use the build-in eq matcher:

it 'returns the created at attribute of a user' do
  get '/users/1'
  
  expect(JSON.parse(response.body)['created_at']).to eq(Time.parse('2001-01-01').to_json)
end

Otherwise the strings do not match:

DateTime.parse('2001-01-01').to_s (will defa...

Sometimes, the rails dev server doesn't terminate properly. This can for example happen when the dev server runs in a RubyMine terminal.

When this happens, the old dev server blocks port 3000, so when you try to start a new server, you get the error:

Address already in use - bind(2) for "127.0.0.1" port 3000 (Errno::EADDRINUSE)

You can terminate such a dev server with this command:

lsof -t -i :3000 -s TCP:LISTEN | xargs kill -9

It might be worth it to add this to your bash aliases.

Let's assume that we have a model Movie that registers a callback function when a new instance of Movie is created (Note: For the purpose of this card it is not important what that callback does or which type of callback it is).

This is how we test whether the callback function (here it is named :my_method) is called when a new movie is created:

expect_any_instance_of(Movie).to receive(:my_method)
create(:movie)  # <-- this is where the method :my_method should be called

You might expect that when calling `create(:mo...

I recently enjoyed debugging a Cucumber step that tried to be retryable using a patiently block:

Then /^"([^"]*)" should( not)? be selected for "([^"]*)"$/ do |value, negate, field|
  patiently do
    field = find(:label, text: field)['for'].delete_suffix('-ts-control')
    ...
  end
end

Unfortunately this block is not retryable:

• The first attempt changes the value of field.
• All subsequent attempts will using the changed value of field, instead of the o...

When an object is created / updated, various callbacks are executed in this order:

before_validation
after_validation
before_save
around_save
before_create
around_create
after_create
after_save
after_commit / after_rollback

Thus, each of these callbacks is executed at a specific time in the life cycle of the object. This is important because this point in time determ...

TLDR

if you define a equality method for a class you must also implement def hash.

Ruby has a lot of methods that have to do something with equality, like ==, ===, eql?, equal?. This card should help you differentiate between those and give you hints on how to implement your own equality methods in a safe manner.

Differences between the methods

for everyday use: ==

When you compare two objects in ruby, you most often see the use of foo == bar. By default the == operator inherits from Object and is impl...

Timecop is a great gem to set the current time in tests. However, it is easy to introduce flakyness to your test suite when you forget to reset the time after the test.
This might be the case if:

• a test freezes time and a later test does not work for frozen time
• a later test needs the real current date to work correctly

Often you only notice these kinds of errors in rare cases when tests are executed in a particular order.

A way to avoid this is by using block notation (`Timecop.travel(...) ...

In a Jasmine spec you want to spy on a function that is imported by the code under test. This card explores various methods to achieve this.

Example

We are going to use the same example to demonstrate the different approaches of mocking an imported function.

We have a module 'lib' that exports a function hello():

// lib.js

function hello() {
  console.log("hi world")
}

export hello

We have a second module 'client' that exports a function helloTwice(). All this does is call hello() ...