title: How to select only specific columns when querying using ActiveRecord?
body: <p>I know if we want to select only some specific columns by using find or where is like this.</p>
  
  <pre><code>Post.find(10).select("column1")
  </code></pre>
  
  <p>But, when I write code like this <code>post.user.username</code> (rely on ActiveRecord associations), if I want to select only a few columns from the <code>user</code> table, I can't find a way to do so.</p>