title: How to customize Rails 3 STI column name
body: <p>I have a class named <code>Post</code>:</p>
  
  <pre><code>class Post &lt; ActiveRecord::Base
  end
  </code></pre>
  
  <p>I have a class named <code>Question</code> that inheriting from <code>Post</code>:</p>
  
  <pre><code>class Question &lt; Post
  end
  </code></pre>
  
  <p>and I have a class named <code>Answer</code> that also inheriting from 'Post':</p>
  
  <pre><code>class Answer &lt; Post
  end
  </code></pre>
  
  <p>In <code>Post</code>, I have a column named <code>post_type_id</code> and its' type is <code>Integer</code>.<br>
  How do I use STI and specific column name &amp; type to inherit from Post? <code>0</code> means <code>Question</code> and <code>1</code> means <code>Answer</code>. (0 &amp; 1 is the value of <code>post_type_id</code> in posts table)</p>