title: How to search structured properties ? google app engine
body: <p>I have two models categories and cities:</p>
  
  <pre><code>class category(ndb.Model):
        hidden = ndb.BooleanProperty()
        categoryName = ndb.StringProperty()
  
  class city(ndb.Model):
        categories = ndb.StructuredProperty(category,repeated = True)
        cityName = ndb.StringProperty()
  </code></pre>
  
  <p>I have cityEntity:
  How to return categories list that contain just category.hidden = false ?</p>
  
  <p>edit:
  it's possible to get the categories list, then Loop through the categories list and extract just the categories which not hidden </p>
  
  <p>for example I have city entity:</p>
  
  <pre><code>categories_unhidden_list = []
  for category in city.categories :
      if not category.hidden :
          categories_unhidden_list.append(category)
  </code></pre>
  
  <p>but I would like to get the categories_unhidden_list from the datastore !</p>