title: Query in NDB database
body: <p>I have an ndb model which has a field </p>
  
  <pre><code> name = ndb.StringProperty(required=True,
         verbose_name=translation.ugettext('Name'))
  tags = ndb.StringProperty(repeated=True)
  </code></pre>
  
  <p>tags may be like (A,B,C,D) so suppose my db have the following values:</p>
  
  <p>Ashish a,b,c,d
  Ankur e,b,c,d
  Ashu g,e,f,g</p>
  
  <p>Now I want a query which will filter according to b in string tags so my desired output for above values will be:</p>
  
  <p>Ashish a,b,c,d
  Ankur e,b,c,d</p>