如何将com.google.appengine.api.datastore.Entity转换为我的实体对象？

Question

Why I get an casting error when I try to get some database object using com.google.appengine.api.datastore.Query

For example: DatastoreService datastore = DatastoreServiceFactory.getDatastoreService(); Query q = new Query("User");

PreparedQuery pq = datastore.prepare(q);

for (Entity entity : pq.asIterable()) {
   User myUser = (User)entity;
}

Answer 1

You can not do that. Entities returned are of type Entity and in java you can not just cast one type to another.

If you want queries to return objects of custom type, you need some kind of mapping framework, for example objectify . It lets you directly use your classes in database operations.