Getting an element by id in Google App Engine's JDO

I have a problem when trying to find a single element by id. The entity class is this:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Test{

   @PrimaryKey
   private String name;

//..and so on.

In this case, the value "name" is acting like an id. I'm using this query to find the element:

           PersistenceManager pm = PMF.get().getPersistenceManager();

           Query q = pm.newQuery(Test.class);
           q.setFilter("name == " + id);

           //String query = "SELECT FROM " + Test.class.getName() + "WHERE name == " + id;
           Test test = (Test) q.execute();

           return category;

Assuming id is a string value 开发者_如何学Csent as a parameter by other method.

But it doesn't retrieve any data. Also, it throws an exception: java.lang.ClassCastException: org.datanucleus.store.appengine.query.StreamingQueryResult cannot be cast to com.santiagopoli.gapptest.domain.Test

The commented query also doesn't work.

I hope anyone can help me. Is a shame that something that basic is difficult to achieve. In other sql implementations, it will be easy as typing "select * from Test where id=". Thanks!

I just fixed it.

Try this...

Test t = pm.getObjectById(Test.class, id);

reference... http://code.google.com/intl/us/appengine/docs/java/datastore/jdo/creatinggettinganddeletingdata.html