.NET/ASP.NET/C#/VB.NET PDF Document SDK

In the last couple sections you ve created a database and migrations to produce a working entries table. In this section you ll create enough code to make a basic Web application that can perform CRUD operations upon data in your entries table. Rails provides a mechanism called scaffolding that generates default, generic code to provide CRUD operations for any of your models. You can then build your own views and controller methods off of this basic scaffolding. It s designed to give you a jump start without making you code everything from scratch (although you can code from scratch if you want to, particularly if your ambitions differ wildly from what the scaffolding provides). To generate scaffolding for your entries table, use the generate script again:

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After quickly digesting the slide, audience attention turns to the speaker and the narration. There is no extraneous information to detract attention.

app/controllers/ app/helpers/ app/views/entries test/functional/ model app/models/ test/unit/ test/fixtures/ app/models/entry.rb test/unit/entry_test.rb test/fixtures/entries.yml app/views/entries/_form.rhtml app/views/entries/list.rhtml app/views/entries/show.rhtml app/views/entries/new.rhtml app/views/entries/edit.rhtml app/controllers/entries_controller.rb test/functional/entries_controller_test.rb app/helpers/entries_helper.rb app/views/layouts/entries.rhtml public/stylesheets/scaffold.css

As you ve seen, exceptions are raised automatically when something is wrong. Before looking at how to deal with those exceptions, let s take a look at how you can raise exceptions yourself and even create your own kinds of exceptions.

When creating scaffolding, Rails looks at the database table associated with the model you re building scaffolding for (the entries table for the Entry model, in this case) and generates a controller, views, and a model file reflecting the structure of the table. The generated files are shown in the preceding results listing.

FIGURE 2-19 A BBP slide, shown here in Normal view, guides the attention of working memory from the

Note Scaffolding depends on the structure of the database table, so you must always create and run the

The scaffolding generator also creates a layout file, several test-related files, and a stylesheet used by the scaffolding layout. It also generates any missing directories needed. That s all you have to do to get a working application! To try it out, you need to run the server script that provides a basic WEBrick Web server through which to access the application:

The simplicity of this slide belies the sophisticated impact it has as it effectively guides the attention of working memory. It is crystal clear where working memory should focus rst on the headline at the top of the slide. People are used to reading newspaper headlines that summarize the main point of a story in a single sentence, and here the complete sentence headline serves the same function. The audience doesn t have to work hard to gure out the point you want to make instead, you have cleared the way for them to focus on the idea at hand rather than be distracted by unnecessary cognitive work.

=> Booting WEBrick... => Rails application started on http://0.0.0.0:3000 => Ctrl-C to shutdown server; call with --help for options [2007-03-19 19:37:48] INFO WEBrick 1.3.1 [2007-03-19 19:37:48] INFO ruby 1.8.5 (2006-08-32) [i686-darwin8.8.1] [2007-03-19 19:37:48] INFO WEBrick::HTTPServer#start: pid=10999 port=3000

To raise an exception, you use the raise statement with an argument that is either a class or an instance. When using a class, an instance is created automatically; you can optionally provide a string argument after the class, separated by a comma. Here are some simple examples, using the built-in exception class Exception: >>> raise Exception Traceback (most recent call last): File "<stdin>", line 1, in Exception >>> raise Exception, 'hyperdrive overload' Traceback (most recent call last): File "<stdin>", line 1, in Exception: hyperdrive overload >>> raise Exception('hyperdrive overload') Traceback (most recent call last): File "<stdin>", line 1, in Exception: hyperdrive overload

At this point the application sits there doing nothing. This is because it s waiting for requests from Web browsers.

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Note If you have the Mongrel library installed, you can use that to serve the Rails application. Just run