Rails has generic error messages you can define in your locale .yml files. You may override those application-wide error messages using model or attribute scope like this:

en:
  activerecord:
    errors:
      messages:
        invalid: is invalid # used for any invalid attribute in the application
        presence: etc
      models:
        car:
          invalid: does not work # used for invalid car attributes
          attributes:
            driver:
              invalid: not allowed to drive # used if the car's driver attribut...

tl;dr

Prefer request specs over end-to-end tests (Capybara) to joyfully test file downloads!

Why?

Testing file downloads via Capybara is not easy and results in slow and fragile tests. We tried different approaches and the best one is just okay.

Tests for file downloads via Capybara ...

• ... are slow,
• ... are fragile (breaks CI, breaks if Selenium driver changes, ...),
• ... need workarounds for your specia...

Add gem 'database_cleaner' to your Gemfile. Then:

Cucumber & Rails 3+

# features/support/database_cleaner.rb

DatabaseCleaner.clean_with(:deletion) # clean once, now
DatabaseCleaner.strategy = :transaction
Cucumber::Rails::Database.javascript_strategy = :deletion

Cucumber & Rails 2

The latest available cucumber-rails for Rails 2 automatically uses database_cleaner when cucumber/rails/active_record is required -- but only if transactional fixtures are off. To have database_cleaner work correctly:

1. Add the ...

Instantiating ActiveRecord objects comes expensive. To speed up things, you can choose a more direct way to talk to your database: the ActiveRecord::ConnectionAdapters::DatabaseStatements module.

Using the module and its methods is not suggested in the usual in-app workflow, as validations, callbacks, custom getters/setters etc. are ignored. However, for database-centered stuff like migrations, these fill the gap between writing pure SQL and full...

Simplecov is a code coverage tool. This helps you to find out which parts of your application are not tested.

Integrating this in a rails project with rspec, cucumber and parallel_tests is easy.

1. Add it to your Gemfile and bundle

   group :test do
     gem 'simplecov', require: false
   end
   

2. Add a .simplecov file in your project root:

   SimpleCov.start 'rails' do
     # any custom configs like groups and filters can be here at a central place
     enable_cov...
   

ActiveRecord computes table names of model classes, and results are usually just like you'd expect.
Adding a prefix for all classes in a namespace can feel a odd or broken, but does not have to be. It's actually very easy when done right.

Summary (tl;dr)

Here's the short version: Define a table_name_prefix method in the namespace module, and do not define any table_name_prefix in ActiveRecord classes inside of it. If this sounds familiar, we have [a card about using it already](https://makandracards.com/makandra/47198-rails-namespac...

PostgreSQL can cosplay as a full-text search engine. It doesn't have the features or fidelity of ElasticSearch or Algolia, but it's good enough if you just need to search and rank large volumes of text.

This card will teach you how to index, search and rank your Rails models in a PostgreSQL full-text index. We will do this without using any gems aside from ActiveRecord. While there are gems like pg_search or pg_fulltext, manual integration requires very...

Rails wraps your parameters into an interface called StrongParameters. In most cases, your form submits your data in a nested structure which goes hand in hand with the strong parameters interface.

Example:

curl -X POST -d "user[name]=bob" https://example.com/users

class UsersController
  def create
    User.create!(params.expect(user: [:name])) # Or User.create!(params.require(:user).permit(:name))
  end
end

This works well most of the time...

I was recently asked to optimize the response time of a notoriously slow JSON API endpoint that was backed by a Rails application.
While every existing app will have different performance bottlenecks and optimizing them is a rabbit hole of arbitrary depth, I'd like to demonstrate a few techniques which could help reaching actual improvements.

The baseline

The data flow examined in this card are based on an example barebone rails app, which can be used to reproduce the r...

It is very common to parse dates from strings. It seems obvious to use Date.parse for this job. However this method does not validate the input and tries to guess the format of the string.

This can lead to a very unexpected results:

Date.parse('Foobar_09_2018')
# Tue, 09 Oct 2018

In most of the cases it would be better to use Date.strptime as you can provide a date or time pattern to match against.

Date.strptime('Foobar_09_2018', '%d_%m_%Y')
# ArgumentError (invalid strptime format - `%d_%m_%Y')

Date.strptime('01_09...

Why Rails has multiple schema formats

When you run migrations, Rails will write your current database schema into db/schema.rb. This file allows to reset the database schema without running migrations, by running rails db:schema:load.

The schema.rb DSL can serialize most common schema properties like tables, columns or indexes. It cannot serialize more advanced database features, like views, procedures, triggers or custom ditionaries. In these cases you must switch to a SQL based schema format:

# in application.rb
config.a...

Rails default config uses the ActiveSupport::Cache::NullStore and disables controller caching for all environments except production:

config.action_controller.perform_caching = false
config.cache_store = :null_store

If you want to test caching you have at least two possibilities:

1. Enable caching for every test (not covered by this card and straightforward)
2. Enable caching for individual test

Enable caching for individual test (file cache)

1. Leave the defau...

TL;DR: Rails ships two methods to convert strings to constants, constantize and safe_constantize. Neither is safe for untrusted user input. Before you call either method you must validate the input string against an allowlist. The only difference between the two methods is that unresolvable constants raise an error with constantize, but return nil with safe_constantize. If you validate the input string against an allowlist, an error should never happen.

Preventing Dangerous Lookups

Suppose an application uses eit...

So you added a new callback to your model that (e.g.) caches some data when it is saved. Now you need to run that callback for the 10000 existing records in the production database. You have two options here:

1. Write a clever migration, possibly by embedding the model into the migration script.
2. Open the Rails console after deployment and re-save every single record. You should probably add two chores to your issue tracker so you won't forget t...

Development environment setup

Rails Composer

Basically a comprehensive Rails Template. Prepares your development environment and lets you select web server, template engine, unit and integration testing frameworks and more.

Generate an app in minutes using an application template. With all the options you want!

Code generators

Rails Bricks

A command line wizard. Once you get it running, it creates sleek applications.

RailsBricks enables you to cre...

If your app does not need to support IE11, you can use most ES6 features without a build step. Just deliver your plain JavaScript without transpilation through Babel or TypeScript, and modern browsers will run them natively.

Features supported by all modern browsers include:

• fat arrow functions (() => { expr })
• let / const
• class
• async / await
• Promises
• Generators
• Symbols
• Rest arguments (...args)
• Destructuring

You won't be able to use import and export, or use npm modules.

See this [ES6 compatibility mat...

Here are some hints on best practices to maintain your tasks in larger projects.

Rake Tasks vs. Scripts

• The Rails default is using rake tasks for your application tasks. These live in lib/tasks/*.
• In case you want to avoid rake for your tasks and just use plain ruby scripts, consider lib/scripts/* as folder.

Keeping tasks slim

For readability and testing it's easier to keep your tasks slim. We suggest to use folders inside the tasks or scripts folder.

Example for a task:

The slim task lib/tasks/gitlab.rb:

Recently we detected a memory leak in one of our applications. Hunting it down, we found that the memory leak was located in Rails' #prepend_view_path. It occurs when the instance method prepend_view_path is called in each request, which is a common thing in a multi-tenant application.

On top of leaking memory, it also causes a performance hit, since templates rendered using the prepended view path will not be cached and compiled anew on each request.

This is not a new memory leak. It was [first reported in in 2014](https://github.com/...

Rails 7.1 added the normalizes method which can be used to normalize user input.

It lets you define the fields you want to normalize and how to normalize them. In the example below, the Movie#title attribute is stripped from leading and trailing whitespace automatically:

class Movie < ApplicationRecord
  normalizes :title, with: -> {  _1.strip }
end

Tip

Normalization lambdas are not called for nil values by default. To normalize nil values, pa...

Rails offers a way to prepend (or append) view paths for the current request. This way, you can make the application use different view templates for just that request.

Example

A use case of this is a different set of view templates that should be used under certain circumstances:

class UsersController < ApplicationController

  before_action :prepare_views
  
  def index
    # ...
  end    
  
  private
  
  def prepare_views
    if <condition>
      prepend_view_path Rails.root.join('app', 'views', 'special')
    end
  end
 ...

If you are using the routing-filter gem in your Rails 7.1 app for managing URL segments for locales or suffixes, you will notice that the filters do no longer apply, routes are broken and the necessary parameters are no longer extracted. That is because routing-filter patches Rails' find_routes-method to get the current path and apply its defined filters on it. These filters then modify the params that are handed over to your controller action. This way you receive a locale parameter from a ...

If you're using a Redis cache in Rails (e.g. :redis_cache_store), it's possible to configure additional parameters for your Redis connection.

Example config for Rails 7.2

config.cache_store = :redis_cache_store, {
  pool: { timeout: 0.5 },
  read_timeout: 0.2, # default 1 second
  write_timeout: 0.2, # default 1 second
  # Attempt two reconnects with some wait time in between
  reconnect_attempts: [1, 5], # default `1` attempt in Redis 5+
  url: REDIS_URL,
  error_handler: ->(method:, returning:, exception:) {
    Sentry.captur...

Rails' default logger prefixes each log entry with timestamp and tags (like request ID).
For multi-line entries, only the first line is prefixed which can give you a hard time when grepping logs.

Example

Rails.logger.info(<<~TEXT)
  Response from example.com:
  Status: 200
  Body: It works!
TEXT

With that, the following is written to your log file.

I, [2024-10-04T08:12:16.576463 #1917250]  INFO -- : [97e45eae-a220-412d-96ad-e9e148ead71d] Response from example.com:
Status: 200
Body: It works!

If you then run `grep...

Upgrade gems

You need to update a lof gems. Make sure you don't have any version constraints in your Gemfile or your bundle update won't do anything!

Upgrade cucumber_priority:

bundle update cucumber_priority

Upgrade spreewald:

bundle update spreewald

Upgrade cucumber_factory:

bundle update cucumber_factory

Upgrade parallel_tests:

bundle update parallel_tests

Even on the latest version, parallel_tests will print some deprecation warnings due to using an older formatter A...