In Rails 2 the only way to add multiple validations to a field is through separate validate statements:
validates_presence_of :title validates_length_of :title, :maximum => 30
Rails 3 simplifies this process by adding a method called validates which is a “shortcut to all default validators”. Using the validates method your code will look like this:
validates(:title, :presence => true, :length => {:maximum => 30})
You can find more information about this method in the API documentation here.
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