Google App Engine（Java）数据存储区检索不起作用

Question

I am not able to retrieve the Entities from Data Store .

Following : Google Code Lab I made this function :

   @SuppressWarnings("deprecation")
   public static Iterable<Entity> listEntities(String kind, String searchBy,String searchFor) {
   com.google.appengine.api.datastore.DatastoreService ds = DatastoreServiceFactory.getDatastoreService();
   Query q = new Query(kind);

   if (searchFor != null && !"".equals(searchFor)) 
        {
            q.addFilter(searchBy, FilterOperator.EQUAL, searchFor);
        }

    PreparedQuery pq = ds.prepare(q);

    return pq.asIterable();

    }

then calling this to get the values :

    for(Entity u:listEntities("Upload","UID","ratan"))
         {
             String uid = (String) u.getProperty("url");
             System.out.println("#1##"+uid);
         }

But it does not prints any value !!! where I went wrong .

this is my Datastore instance for "Upload" Entity

Even this doesn't works:

for(Entity u:listEntities("Upload",null,null))
{
  String uid = (String) u.getProperty("url");
  System.out.println("#1##"+uid);
}

Answer 1

You have to define index for this entity. How to define index in app engine please look at this link:

https://developers.google.com/appengine/docs/java/config/indexconfig