title: Compatibility of ndb models with WTForms
body: <p>Tech Stack: <strong>ndb models</strong>, <strong>WTForms</strong>, <strong>webapp2</strong> 
  I was experimenting with the WTForms extension to appengine db models. </p>
  
  <p>I had a simple db schema:</p>
  
  <pre><code>class Autho(ndb.Models):
      name = db.StringProperty()
  
  class Notes(ndb.Model):
      title = db.StringProperty()
      author = db.KeyProperty()
  </code></pre>
  
  <p>and then a simple form definition form WTForms, in the handlers as per their documentation:</p>
  
  <pre><code>from wtforms.ext.appengine.db import model_form
  
  def get(self, slug):
          form = model_form(Author)()
          self.render_template('form.html', {'form': form})
  </code></pre>
  
  <p>This raises an Attribute Error line 411 <a href="https://bitbucket.org/simplecodes/wtforms/src/a5f9e30260cc/wtforms/ext/appengine/db.py" rel="nofollow">here</a> <code>props = model.properties()</code></p>
  
  <p>Please let me know, if this can be fixed. </p>