title: How to delete a record using GQL?
body: <p>I need to iterate and delete all records of my datastore. I am using Google App engine Launcher to test it on local host. How to do it?</p>
  
  <p>When I am trying to delete all recors in Person model that way:</p>
  
  <pre><code> qObj = Person.all()
   db.delete(qObj)
  </code></pre>
  
  <p>I am getting error <code>BadValueError: Property y must be a str or unicode instance, not a long</code>
  I guess there is conflict in Model data types.</p>
  
  <pre><code>class Person(db.Model):
      name = db.StringProperty()
      x = db.StringProperty()
      y = db.StringProperty()
      group = db.StringProperty()
  </code></pre>
  
  <p>The field <code>y = db.StringProperty()</code> previously was <code>y = db.IntegerProperty()</code>.
  At this moment I need to flush all db records. How can I do that?</p>
  
  <p>Is there is an opportunity to delete local file which stores all db records?</p>