Lesson 2 -- Databases

In writing software for any platform, we need to be able to do 3 things:
1. get input from the user
2. store the information
3. output results to the user

We have , on the Rails platform, learnt how to output text to the user 
via a dynamic web page. In this chapter we deal with databases. In the 
next chapter, we will see how to get input from the user, and you will be 
ready to start writing your application.

Imagine we wish to create a database for books, and wish to track their 
names, numbers and authors. In Rails, we simply, on the command line,
go to the root folder of the application, and type the following 

script/generate scaffold book name:string num:integer author:string
rake db:create
rake db:migrate

now, assuming the server is still running from the previous chapter, 
fire up your browser and go to http://localhost:3000/books/ and you
will be pleasantly surprised to find that you not only have a 
functioning database, but also a minimal application that allows you 
to add edit and destroy records in this database. Click on "new book" 
to come to http://localhost:3000/books/new where you see a regular 
data entry screen for the name, number and author of the book you wish 
to enter into the database.

How do we use the database in our own programming? Next chapter. For now, 
let me leave you with the output of the above commands, to help you 
diagnose the fault if things go wrong. 

>script/generate scaffold book name:string num:integer author:string
      exists  app/models/
      exists  app/controllers/
      exists  app/helpers/
      create  app/views/books
      exists  app/views/layouts/
      exists  test/functional/
      exists  test/unit/
      exists  public/stylesheets/
      create  app/views/books/index.html.erb
      create  app/views/books/show.html.erb
      create  app/views/books/new.html.erb
      create  app/views/books/edit.html.erb
      create  app/views/layouts/books.html.erb
   identical  public/stylesheets/scaffold.css
      create  app/controllers/books_controller.rb
      create  test/functional/books_controller_test.rb
      create  app/helpers/books_helper.rb
       route  map.resources :books
  dependency  model
      exists    app/models/
      exists    test/unit/
      exists    test/fixtures/
      create    app/models/book.rb
      create    test/unit/book_test.rb
      create    test/fixtures/books.yml
      exists    db/migrate
      create    db/migrate/20090511140924_create_books.rb

>rake db:create
(in /home/user/ruby/code/test)
db/development.sqlite3 already exists

>rake db:migrate
(in /home/user/ruby/code/test)
== 20090511140924 CreateBooks: migrating ======================================
-- create_table(:books)
   -> 0.2238s
== 20090511140924 CreateBooks: migrated (0.2250s) =============================

Again, just 3 lines of typing!