Just want to know how Rails "magic" actually works.
- ActiveSupport - is a compatibility library including methods that aren't necessarily specific to Rails. You'll see ActiveSupport used by non-Rails libraries because it contains such a lot of useful baseline functionality. ActiveSupport includes methods like how Rails changes words from single to plural, or CamelCase to snake_case. It also includes significantly better time and date support than the Ruby standard library.
- ActiveModel - hooks into features of your models that aren't really about the database - for instance, if you want a URL for a given model, ActiveModel helps you there. It's a thin wrapper around many different ActiveModel implementations to tell Rails how to use them. Most commonly, ActiveModel implementations are ORMs (see ActiveRecord, below), but they can also use non-relational storage like MongoDB, Redis, Memcached or even just local machine memory.
- ActiveRecord - is an Object-Relational Mapper (ORM). That
means that it maps between Ruby objects and tables in a
SQL database. When you query from or write to the SQL database in Rails, you do it through ActiveRecord.
ActiveRecord also implements ActiveModel. ActiveRecord supports MySQL and SQLite, plus JDBC, Oracle, PostgreSQL and many others. - ActionPack does routing - the mapping of an incoming URL to a controller and action in Rails. It also sets up your controllers and views, and shepherds a request through its controller action and then through rendering the view. For some of it, ActionPack uses Rack. The template rendering itself is done through an external gem like Erubis for .erb templates, or Haml for .haml templates. ActionPack also handles action- or view-centered functionality like view caching.
- ActionMailer - is used to send out email, especially email based on templates. It works a lot like you'd hope Rails email would, with controllers, actions and "views" - which for email are text- based templates, not regular web-page templates.