title: Custom error messages in rails 3
body: <p>I have the following validation. I am using the new sintaxis of Ruby on Rails, where can be declared many validations to a same attribute, but I need a custom error message for each validation </p>
  
  <pre><code>validates :user_name, presence: true, uniqueness: true
  
  
    for example  validates_presence_of :user_name, message: "Can not be empty"
                 validates_uniqueness_of :user_name, message: "Must to be unique"
  </code></pre>