title: auto field values in ndb.StructuredProperty
body: <p>I want to store locations in google's datastore. Each entry shall have got 'sys'-fields, which shall contain information set by the datastore.
  I've got the class model below and the WebService JSON request/response looks ok, but I have to set the values manually. It looks like <code>auto_current_user_add</code>, <code>auto_now_add</code>, <code>auto_current_user</code> and <code>auto_now</code> does not trigger.</p>
  
  <pre><code>from google.appengine.ext import ndb
  from endpoints_proto_datastore.ndb import EndpointsModel
  
  
  class Created(EndpointsModel):
      by = ndb.UserProperty(auto_current_user_add=True)
      on = ndb.DateTimeProperty(auto_now_add=True)
  
  
  class Updated(EndpointsModel):
      by = ndb.UserProperty(auto_current_user=True)
      on = ndb.DateTimeProperty(auto_now=True)
  
  
  class Sys(EndpointsModel):
      created = ndb.StructuredProperty(Created)
      updated = ndb.StructuredProperty(Updated)
  
  
  class Location(EndpointsModel):
      name = ndb.StringProperty(required=True)
      description = ndb.TextProperty()
      address = ndb.StringProperty()
      sys = ndb.StructuredProperty(Sys)
  </code></pre>
  
  <p>When I submit a create request (<code>location.put()</code>) I get the following response:</p>
  
  <pre><code>{
      "id": "4020001",
      "name": "asdf"
  }
  </code></pre>
  
  <p>When I set it manually using:</p>
  
  <pre><code>location.sys = Sys(created=Created(on=datetime.datetime.now(),
                                     by=current_user),
                     updated=Updated(on=datetime.datetime.now(),
                                     by=current_user))
  location.put()
  </code></pre>
  
  <p>I get the expected result:</p>
  
  <pre><code>{
   "id": "4020002",
   "name": "asdf",
   "sys": {
    "created": {
     "by": {
      "auth_domain": "gmail.com",
      "email": "decurgia@XYZ"
     },
     "on": "2015-01-27T16:05:41.465497"
    },
    "updated": {
     "by": {
      "auth_domain": "gmail.com",
      "email": "decurgia@XYZ"
     },
     "on": "2015-01-27T16:05:41.465577"
    }
   }
  }
  </code></pre>
  
  <p>How can I get those fields (<code>sys.created.on</code>, <code>sys.created.by</code>, <code>sys.updated.on</code>, <code>sys.updated.by</code>) automatically set?</p>