ch11-default-initializers.md

<< Startup Scripts | README | Other Common Initializers >>

Chapter 11. Default Initializers

The config/initializers directory contains a set of default init scripts. Remember that you need to restart your server when you modify any of these files.

You can and should add configs for your own app by adding your own scripts to the initializers directory.

config/initializers/application_controller_renderer.rb

View rendering is covered in depth in the Action View chapter. Rails 5 introduces the ActionController::Renderer class as a utility for rendering arbitray templates' absent controller actions, like rendering a PDF report in a background job.

Templates are rendered in a context with supplementary data. Like if a view template needs to create a URL, how will it know the hostname, or whether to use SSL.

The application_controller_renderer.rb script provides a place for setting those kinds of defaults.

# ApplicationController.renderer.defaults.merge!(
#   http_host: 'example.org',
#   https: false
# )

config/initializers/assets.rb

The Asset Pipeline has a number of settings that allow you to customize its behavior. You can view those in the Asset Pipeline Configuration.

# Version of your assets, change this if you want to expire all your assets.
Rails.application.config.assets.version = '1.0'

# Add additional assets to the asset load path
# Rails.application.config.assets.paths << Emoji.images_path

# Precompile additional assets.
# application.js, application.css, and all non-JS/CSS in app/assets folder are already added.
# Rails.application.config.assets.precompile += %w( search.js )

config/initializers/backtrace_silencers.rb

Nobody likes really long exception backtraces. Rails actually gives you a built-in mechanism for reducing the size of backtraces that contain lines which aren't useful.

It lets you modify the way way that backtraces are shortened. You should never need to remove all silences during normal application development.

config/initializers/cookies_serializer.rb

Since browser cookies are simply string-based key-value pairs, then storing anything other than strings requires serialization. This setting controls how Rails handles that serialization behavior.

# Specify a serializer for the signed and encrypted cookie jars.
# Valid options are :json, :marshal, and :hybrid.
Rails.application.config.action_dispatch.cookies_serializer = :json

Note that applications created before Rails 4.1 use Ruby's built-in Marshal class to serialize cookie values. If you are upgrade to Rails 5 and want to transparently migrate your existing Marshal-serialized cookies into the new JSON-based format, you can set it to :hybrid.

Rails.application.config.action_dispatch.cookies_serializer = :hybrid

When using either serializer, you should be aware that not all Ruby objects can be natively serialized as JSON. Like Date and Time objects will be serialized as strings, and Hashes will have symbolic keys stringified.

config/initializers/filter_parameter_logging.rb

When a request is made to your application, Rails logs all such details. This lets you specify what request parameters should be filtered from your log files.

config/initializers/inflections.rb

Rails has a class named Inflector whose job is to transform strings from singulare to plurals, class names to table names, modulared class names to ones without, and class names to foreign keys, etc.

The default inflections are kept in a file inside the ActiveSupport gem, inflections.rb.

Most of the time it does a decent job of figuring out the pluralized table name for a given class, but it's not guaranteed.

ActiveSupport::Inflector.pluralize "project"
# => "projects"
ActiveSupport::Inflector.pluralize "virus"
# => "viri"
"pensum".pluralize  # Inflector features are mixed into String by default
# => "pensums"

To see the test cases, view the inflector_test_cases.rb file.

config/initializers/mime_types.rb

Rails supports the standard set of MIME types. If your app needs to response to other MIME types, you can register them in this initializer.

config/initializers/new_framework_defaults.rb

This contains migration options that promise to ease the move to Rails 5 from earlier versions. See the related chapters for more details of these commands.

# Enable per-form CSRF tokens. Previous versions had false.
Rails.application.config.action_controller.per_form_csrf_tokens = true

# Enable origin-checking CSRF mitigation. Previous versions had false.
Rails.application.config.action_controller.forgery_protection_origin_check = true

# Make Ruby 2.4 preserve the timezone of the receiver when calling `to_time`.
# Previous versions had false.
ActiveSupport.to_time_preserves_timezone = true

# Require `belongs_to` associations by default. Previous versions had false.
Rails.application.config.active_record.belongs_to_required_by_default = true

# Do not halt callback chains when a callback returns false. Previous versions had true.
ActiveSupport.halt_callback_chains_on_return_false = false

# Configure SSL options to enable HSTS with subdomains. Previous versions had false.
Rails.application.config.ssl_options = { hsts: { subdomains: true } }

config/initializers/session_store.rb

Rails session cookies are encrypted by default using an encrypted cookie store. This initializer configures the session store of the app.

The session cookies are signed using the secret_key_base set in the config/secrets.yml file. You can change that key manualls, or run rake secret to generate a new one automatically.

config/initializers/wrap_parameters.rb

Introduced in Rails 3.1, this initializer configures your app to work with many JS frameworks out of the box.

# Be sure to restart your server when you modify this file.

# This file contains settings for ActionController::ParamsWrapper which
# is enabled by default.

# Enable parameter wrapping for JSON. You can disable this by setting
# :format to an empty array.
ActiveSupport.on_load(:action_controller) do
  wrap_parameters format: [:json]
  end

# To enable root element in JSON for ActiveRecord objects.
# ActiveSupport.on_load(:active_record) do
#  self.include_root_in_json = true
# end

When submitting JSON params to a controller, Rails will wrap the params into a nested hash, with the controller's name being set as the key, so that the controller can treat JS clients and HTML forms identically. This ensures the setting of model attributes from request params is consistent with the Rails form helper convention.

{"title": "The Rails 5 Way"}

If a client submitted the above via JSON to an ArcticlesController, Rails would nest the params hash under the key "article".

{"title": "The Rails 5 Way", "article" => {"title": "The Rails 5 Way"}}

<< Startup Scripts | README | Other Common Initializers >>