Ruby on Rails 5.0: What's New, Release History & Support Lifecycle

What Is New in Ruby on Rails 5.0

How does Action Cable enable real-time features in Rails 5?

Action Cable integrates WebSockets directly into the Rails stack, letting you write real-time channels in pure Ruby.

• Server-side channels inherit from ApplicationCable::Channel and have full access to Active Record models.
• Client-side JavaScript uses a built-in consumer that connects to /cable automatically.
• Scalable deployment works with any Rack-compatible server; you can run multiple workers behind a Redis pub/sub backend.

# app/channels/chat_channel.rb
class ChatChannel < ApplicationCable::Channel
  def subscribed
    stream_from "chat_#{params[:room]}"
  end

  def receive(data)
    ActionCable.server.broadcast("chat_#{params[:room]}", data)
  end
end

What is the API-only mode and how do I generate an API-only Rails app?

Rails 5 can generate a lean stack that omits view-related middleware, helpers, and assets, perfect for JSON APIs.

• Run rails new my_api --api to create the skeleton.
• The generated ApplicationController inherits from ActionController::API, not ActionController::Base.
• Middleware such as ActionDispatch::Cookies and Rack::MethodOverride are excluded by default.
• Generators skip views, helpers, and assets unless you explicitly add them back.

# config/application.rb
module MyApi
  class Application < Rails::Application
    config.api_only = true
  end
end

How does the new Active Record attributes API change type casting and defaults?

The attributes API lets you declare typed attributes, custom defaults, and even virtual columns without database backing.

• Use attribute :price_in_cents, :integer to override the default decimal type.
• Supply a default value or a proc: attribute :published_at, :datetime, default: -> { Time.current }.
• Define virtual attributes that are serialized/deserialized automatically, e.g., attribute :tags, :string, array: true.
• Custom types can be created by subclassing ActiveModel::Type::Value and implementing cast and serialize.

# app/models/product.rb
class Product < ApplicationRecord
  attribute :price_in_cents, :integer
  attribute :status, :string, default: "draft"
end

product = Product.new(price_in_cents: "1999")
product.price_in_cents # => 1999

What are the key deprecations and removals that can break existing apps when upgrading to Rails 5?

Several long-standing APIs were removed or deprecated, and they will raise errors if your code still relies on them.

• Debugger support was dropped; replace debugger with the byebug gem.
• respond_to and respond_with were extracted to the responders gem.
• Deprecated *_filter callbacks; migrate to *_action equivalents.
• Old redirect_to :back is gone; use redirect_back fallback_location: root_path.
• ActionDispatch::ParamsParser was removed from the middleware stack; configure parsers via ActionDispatch::Request.parameter_parsers=.

How does the new test runner improve the developer workflow?

The built-in test runner invoked with bin/rails test adds flexible options and better output for Minitest suites.

• Run a single test by appending :line_number (e.g., bin/rails test test/models/user_test.rb:42).
• Use -f for fail-fast, -d to defer output, -b for full backtraces, and -v for verbose mode.
• Colored output makes failures stand out in the terminal.
• Integration with Minitest options like -n (run by name) and -s (seed) is seamless.

# Run all tests with verbose output and fail fast
bin/rails test -v -f