title: Create an array before saving/validation
body: <p>I'm using selectize gem for this task and can't understand how to add values without <code>{}</code> to those would be saved correctly. I have <code>array: true</code> on this column, so values must be sent in an array, not the string.</p>
  
  <p>I tried convert this attribute before saving of record, but still no result.</p>
  
  <pre><code>class Post &lt; ActiveRecord::Base
    before_validation :convert_to_array
  
    def convert_to_array
      self.tags = tags.split(",")
    end
  end
  </code></pre>
  
  <p>Error</p>
  
  <pre><code>ERROR:  malformed array literal: "{{}}"
  </code></pre>
  
  <hr>
  
  <p>If there aren't callbacks</p>
  
  <pre><code>    Parameters: {"post"=&gt;{"title"=&gt;"Aliquam laborum consequatur voluptatem quo.",
  "tags"=&gt;"asdas,zxzx"}, "_wysihtml5_mode"=&gt;"1", "commit"=&gt;"Save", "id"=&gt;"4"}
  </code></pre>