title: Quickest way to redefine field in Flask-Admin for custom type
body: <p>I use Flask-Admin + SqlAlchemy + PostgreSQL. What I'm going to do is the following: I want to store timezone selected by user via this <a href="http://www.jqueryscript.net/demo/Easy-Timezone-Picker-with-jQuery-Moment-js-Timezones/" rel="nofollow">Jquery Timezones Plugin</a> as Interval in database. When user create new entry, we should guess his timezone (that's what this plugin does by default), if user edit entry - we should show its time zone.</p>
  
  <p>When I used String for keeping timezone, I decided to make dirty hack - wrap my field, hide it and add another one below, which is initiated by timezone plugin.</p>
  
  <pre><code>rules.Container('time_zone.wrap', rules.Field('time_zone'))
  </code></pre>
  
  <p>But when I switched from String to Interval, I experienced the following error:</p>
  
  <pre><code>ValueError: Form &lt;flask_admin.contrib.sqla.form.MyForm object at 0x7fe4fd967690&gt; does not have field time_zone
  </code></pre>
  
  <p>So, it looked for me that Flask-Admin doesn't support working with field for Interval type natively. I then tried to use rules.Macro, but I'm not sure how can I pass current time_zone value via form_create_rules or how can I get it from create/macro template (that's needed in case of editing entry).</p>
  
  <p>Anyway, I need the quickest way to implement it (I'm OK if solution will be not as good as possible).</p>
  
  <p>Any ideas?</p>