title: Rails check_box_tag checked according boolean value
body: <p>In my db, I've a boolean field: <code>is_in_city</code>.</p>
  
  <p>In view, I try to set <code>check_box_tag</code> as:</p>
  
  <pre><code>= check_box_tag c.is_in_city
  </code></pre>
  
  <p>But it is never checked even if the db value is true. What is wrong?</p>
  
  <p>I need to do such <code>chekbox</code>, which is no/is checked according to db boolean field value stored in the database. How can I do this? Also how can I set one more my property to checkbox?</p>