title: How to use validates_unique in Sequel validation_helpers plugin
body: <p>I am actually using Sequel plugin validation_helpers, and i did not have any problem using the validates_presence option. But when i try to use validates_unique it does not do anything.
  I tried to put UNIQUE on my columns, but it raise an error and i just want an error in my sent message.
  Here is what i did so far:</p>
  
  <pre><code>class User &lt; Sequel::Model
    plugin :validation_helpers
    def validates
       super
       validates_presence[:username, :email]
       validates_unique(:username)
    end
  end
  </code></pre>
  
  <p>So when i "forget" to put either a username or a mail it send an error Json object, but i can post as much user with the same username as i want.</p>
  
  <p>So... Do someone can think about a solution?</p>