Ruby on Rails® for Microsoft Developers

5.8. Adding Validations

Validations are a mechanism provided by Active Record to ensure that the data conforms to certain business rules. The forms generated by the scaffold generator don't perform any validations by default. For example, you could create an article that had an empty title and empty body, and these would be stored in the database as empty strings. Similarly, you may decide that you don't want to allow articles to have the same exact text, therefore eliminating duplicates. Validations are the answer.

Change the Article model to look like this (app\models\article.rb):

class Article < ActiveRecord::Base
  validates_presence_of :title, :body
  validates_uniqueness_of :body
end

Those two highlighted lines indicate that an article's title and a body are required and that the body of an article needs to be different from any others that already exist. Save the file, head over to /articles/new, and try to click Create Article with the title and body left empty. You should see an error report similar to the one shown in Figure 5-12.

NOTE

Unlike ASP.NET validation controls, Rails validations are always server-side and defined in the model, as opposed to the page that gets rendered.

Figure 5.12. Figure 5-12

That was quite effortless! If you take a look at the source of the generated page, you will see that the <%= f.error_messages %> inside the partial was transformed into ...