Get datastore element by id

[Santiago Poli]

Hello everyone. 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 == " + category_id);

//String query = "SELECT FROM " + JokeCategory.class.getName() + "
WHERE name == " + category_id;
JokeCategory category = (JokeCategory) q.execute();

return category;

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=<id>". Thanks!

[Nick Johnson (Google)]

Hi Santiago,

Please see the section of the docs titled "Getting an object by key": http://code.google.com/appengine/docs/java/datastore/jdo/creatinggettinganddeletingdata.html#Getting_an_Object_By_Key

-Nick Johnson

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