For example, suppose that you have 5 models, with the following hierarchy:
class Author < ActiveRecord::Base end class BankAccount < ActiveRecord::Base end class Book < ActiveRecord::Base establish_connection "library_db" end class ScaryBook < Book end class GoodBook < Book end
And a database.yml that looked like this:
development: database: my_application host: localhost library_db: database: library host: some.library.org
Your primary database in the development environment is “my_application” but the Book model connects to a separate database called “library_db” (this can even be a database on a different machine).
Book, ScaryBook and GoodBook will all use the same connection pool to “library_db” while Author, BankAccount, and any other models you create will use the default connection pool to “my_application”.
The various connection pools are managed by a single instance of ConnectionHandler accessible via ActiveRecord::Base.connection_handler. All Active Record models use this handler to determine the connection pool that they should use.