title: Querying for a value existing in a model's list property in AppEngine
body: <p>A sample model:</p>
  
  <pre><code>  class Foo(db.Model):
       id = db.IntegerProperty()
       bar = db.ListProperty(int, required=True)
  </code></pre>
  
  <ol>
  <li><p>How can I query using either Query or GqlQuery to return all <strong>Foo</strong> entities that have a given value in their <strong>bar</strong> property?</p></li>
  <li><p>If I have a list of ids, is there a single filter that will return all entities whose <strong>id</strong> property is in that list?</p></li>
  </ol>