ASP.NET Web PDF Document Viewer/Editor Control Library

Rails operates upon a Model-View-Controller (MVC) architectural pattern. This means that Rails applications are primarily split into three sections: models, views, and controllers. In Rails, these components have the following roles: Models: These are used to represent forms of data used by the application and contain the logic to manipulate and retrieve that data. In Rails, a model is represented as a class. You can think of models as abstracted, idealized interfaces between controller code and data. Views: These are the templates and HTML code that users of the Web application see. They turn data into a format that users can view. They can output data as HTML for Web browsers, XML, RSS, and other formats. Controllers: Controllers form the logic binding together models, data, and views. They process input and deliver data for output. Controllers call methods made available by models and deliver it to the views. Controllers contain methods known as actions that, generally, represent each action relevant to that controller, such as show, hide, view, delete, and so forth. The basic relationship between these components is shown in Figure 13-1.

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Note You can learn more about the MVC paradigm at http://en.wikipedia.org/wiki/

The most common motivation to use Rails is that it removes a lot of the groundwork necessary to develop Web applications using other technologies. Features such as database access, dynamic page elements (using Ajax Asynchronous JavaScript and XML), templating, and data validation are either preconfigured or take only a few lines of code to configure. Rails also encourages good development practices. All Rails applications come with support for unit testing (among other forms of testing), and Rails guiding principles are Don t Repeat Yourself (known as DRY) and Convention Over Configuration.

The Rails framework is made up of several different libraries, but it s simple to install because all the parts are distributed as RubyGems. For completeness, though, the following is a list of Rails constituent libraries: Rails: The core library of the Ruby on Rails framework that ties the other libraries together. ActionMailer: A library that makes it easy to send e-mail from Rails applications. A basic overview of ActionMailer, including how to use it to send mail separately from Rails, is given in 14.

Although text on a screen is a visual element, working memory quickly verbalizes the words and sends them through the verbal channel. Research over the years has found that the way information is presented to these two channels has a big impact on the effectiveness of working memory. See Also For more information about the dual-channels concept, see: Alan D. Baddeley and Graham Hitch, Working Memory, in The Psychology of Learning and Motivation: Advances in Research and Theory, G. H. Bower, Ed., Vol. 8, pp. 47 89 (Academic Press, 1974). Allan Paivio, Mind and Its Evolution (Lawrence Erlbaum Associates, 2007).

Instead of just calling the methods and hoping for the best, you can check whether the required methods are present and if not, perhaps do something else: >>> hasattr(tc, 'talk') True >>> hasattr(tc, 'fnord') False In the preceding code, you find that tc (a TalkingCalculator, as described earlier in this chapter) has the attribute talk (which contains a method), but not the attribute fnord. If you wanted to, you could even check whether the talk attribute was callable: >>> callable(getattr(tc, 'talk', None)) True >>> callable(getattr(tc, 'fnord', None)) False Note that instead of using hasattr in an if statement and accessing the attribute directly, I m using getattr, which allows me to supply a default value (in this case None) that will be used if the attribute is not present. I then use callable on the returned object.