Middleman is a static page generator that brings many of the goodies that Rails developers are used to.

Out of the box, Middleman brings Haml, Sass, helpers etc. However, it can be configured to do even better. This card is a list of improvement hints for a Rails developer.

Gemfile

Remove tzinfo-data and wdm unless you're on Windows. Add these gems:

gem 'middleman-livereload'
gem 'middleman-sprockets' # Asset pipeline!

gem 'bootstrap-sass' # If you want to use Bootstrap

gem 'byebug'

gem 'capistrano'
gem 'capistrano-mid...

If you have any class which requires access to some path methods generated by your routes. Even though you could technically include Rails.application.routes.url_helpers, this may include way too many methods and even overwrite some class methods in the worst case.

Instead, most of the time the following is advised to only make the desired methods available:

class Project
  delegate :url_helpers, to: 'Rails.application.routes'

  def project_path
    url_helpers.project_path(self)
  end
end

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...

Modern IRB has time measurement built in.

measure # Enable
measure :off # Disable

Custom

Should your version of IRB not offer this feature, you can measure manually. Paste this method into your console:

def time(&block) puts Benchmark.measure(&block) end

Now time { Some.lengthy_task } will behave similar to the bash time command. Of course you can do much more with the Benchmark object than just putsing it – adapt to your needs.

Code snippet tested with Rails 2.3

  def index
    # ...
    if request.xhr?
      html = render_to_string(:partial => "list", :layout => false)
      respond_to do |format|
        format.html { render :text => html }
        format.json { render :json => {:html => html, ... } }
      end
    end
  end

Note: Perhaps you ran into ActionView::MissingTemplate error and this card might help. If you call render_to_string within the format.json block, Rails will only look for an index.json template, but not for an `index.erb...

Sometimes it is useful to define a named scope by implementing a static method with the scope's name on the scoped class. For instance, when a method should decide which existing scope should be the next link in the scope chain. Take this class for example:

class Meal < ActiveRecord::Base

  named_scope :for_date, lambda { |date| :conditions => { :date => date }}
  named_scope :with_meat, :conditions => { :meat => true }
  named_scope :without_meat, :conditions => { :meat => false }

  def self.suitable_for(user)
    if user.vegetar...

tl;dr

Since Rails 7+ you can use ComparisonValidator for validations like greater_than, less_than, etc. on dates, numerics or strings.

Example

We have a model for booking a trip. This model has mandatory attributes to enforce dates for the start and the end.

# == Schema Information
#
# start_date :date
# end_date   :date
# ...

class TripBooking < ApplicationRecord
  validates :start_date, presence: true
  validates :end_date, presence: true
end

These validations are enough. We also want to ensure, th...

In case you have trouble with the zeitwerk autoloader, you can check out the documentation Autoloading and Reloading Constants and Classic to Zeitwerk HOWTO for some debugging hints.

For myself it was useful to print the registered constants and the file references during the boot. Therefore you need to add Rails.autoloaders.log! at the end of your config/application.rb file. You could also run `bin...

For Rails models where only one of multiple attributes may be filled out at the same time, there is no built-in validation.

I've seen different solutions in the wild, each with different downsides:

• Private method referenced via validate: works, but is barely portable and clutters the model.
• Multiple presence validations with "if other is blank" each: looks pretty, but is incorrect as it allows both values to be filled in; also the error messages for a blank record are misleading.

Here is a third option: Write a custom validator to ...

In this example we assume that not only the storage gem changes but also the file structure on disc.

A general approach

Part A: Create a commit which includes a script that allows you to copy the existing file to the new file structure.

Part B: Create a commit which removes all paperclip logic and replace it with the same code you used in the first commit

Part A

Here are some implementation details you might want to reuse:

• Use the existing models to read the files from
• Use your own carrierwave models to write t...

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.

There are a few tools to combat the dreaded n+1 queries. The bullet gem notifies you of missing eager-loading, and also if there is too much eager-loading. strict_loading in Rails 6.1+ forces developers to explicitly load associations on individual records, for a single association, for an entire model, or globally for all models.

But you can also actually **write spe...

tl;dr

Since Rails 6.1+ you can use .compact_blank or .compact_blank! to remove blank values from collections (e.g. arrays).

Remove nil values from an array

['foo', nil].compact
# => ['foo']

# You can use the splat operator to ignore nil values when constructing an array
['foo', *nil]
# => ['foo']

Remove blank values from collections

Array

array = [1, "", nil, 2, " ", [], {}, false, true]

# Any Rails version
array.reject(&:blank?)
# => [1, 2, true]

# Since Rails 6.1+
array.compact_blank
# ...

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...

Within development and test environments, Rails is usually configured to show a detailed debug page instead of 404s. However, there might be some cases where you expect a 404 and want to test for it.

An example would be request-specs that check authorization rules. (If you use a gem like consul for managing authorization rules, you should always check these rules via power-specs. However, request-specs can be used as a light-weight version of integration tests here.)

In this case, Rails will replace the 404 page that you want to test ...

The problem

When using the asset pipeline your assets (images, javascripts, stylesheets, fonts) live in folders inside app:

app/assets/fonts
app/assets/images
app/assets/javascripts
app/assets/stylesheets

With the asset pipeline, you can use the full power of Ruby to generate assets. E.g. you can have ERB tags in your Javascript. Or you can have an ERB template which generates Haml which generates HTML. You can chain as many preprocessors as you want.

When you deploy, Rails runs assets:precompile...

Webpacker is Rails' way of integrating Webpack, and version 4 has been released just a few days ago, allowing us to use Webpack 4.

I successfully upgraded an existing real-world Webpack 3 application. Below are notes on everything that I encountered.
Note that we prefer not using the Rails asset pipeline at all and serving all assets through Webpack for the sake of consistency.

Preparations

• Remove version locks in Gemfile for webpacker
• Remove version locks in package.json for webpack and webpack-dev-server
• Install by ca...

Note: Instead of using the method in this card, you probably want to use ActiveType's nested attributes which is a much more refined way of doing this.

The attached Modularity trait allows you to accept nested attributes for a record that is not an association, e.g.:

    class Site < ActiveRecord::Base
      
      def home_page
        @home_page ||= Page.find_by_name('home')
      end
      
      does 'a...

A memory leak is an unintentional, uncontrolled, and unending increase in memory usage. No matter how small, eventually, a leak will cause your process to run out of memory and crash.

If you have learned about a memory leak, looking at the number of Ruby objects by type can help you track it down:

> pp ObjectSpace.count_objects
{:TOTAL=>77855,
 :FREE=>4526,
 :T_OBJECT=>373,
 :T_CLASS=>708,
 :T_MODULE=>44,
 :T_FLOAT=>4,
 :T_STRING=>65685,
 :T_REGEXP=>137,
 :T_ARRAY=>984,
 :T_HASH=>87,
 :T_STRUCT=>12,
 :T_BIGNUM=>2,
 :T_FILE=>3,
 :T_D...

When you're writing migrations that do more than changing tables (like, modify many records) you may want some output. In Rails > 3.1 you have two methods at hand: announce and say_with_time.

In the migration:

class AddUserToken < ActiveRecord::Migration

  class User < ActiveRecod::Base; end

  def up
    add_column :users, :token, :string
    
    announce "now generating tokens"
    User.find_in_batches do |users|
      say_with_time "For users ##{users.first.id} to ##{users.last.id}" do
        users.each do |user|
        ...

Imagine these models and associations:

class Deck < ApplicationRecord
  has_many :cards
end

class Card < ApplicationRecord
  belongs_to :deck, optional: true
end

Now you want to find all Decks without any Card or all Cards without a Deck.

Rails 6.1+

Rails 6.1 introduced a handy method ActiveRecord#missing to find records without given associations.

Deck.where.missing(:cards)

SELECT "decks".*
FROM "dec...

If validations failed for a record, and you want to find out if a specific validation failed, you can leverage ActiveModel's error objects.
You rarely need this in application code (you usually just want to print error messages), but it can be useful when writing tests.

As an example, consider the following model which uses two validations on the email attribute.

class User < ApplicationRecord
  validates :email, presence: true, uniqueness: true
end

Accessing errors

Let's assume we have a blank user:

user = Us...

When redirecting you should take care to use the right HTTP status code.

From controllers

When redirecting from a controller, the default status code is 302 Found (aka Moved Temporarily):

red...

ActionMailer per default uses http as protocol, which enables SSL-stripping. When a logged-in user follows an http link to your application, it sends the cookies along with it. Although the application redirects the user to https and from that point has a secure connection to the user, an attacker may overhear that first unsafe request and hijack your session.

Teach ActionMailer to use the right protocol

If your application is behind SSL, turn on using https application-wide. In your environment file (either global or per environ...