JDO Query - Find error

[Benjamin Lietzau]

Hello,

I get following error:

Problem with query <SELECT FROM de.hsowl.google.evaluation.model.Appointment WHERE userPara == createdBy PARAMETERS String userPara>: Unexpected expression type while parsing query: org.datanucleus.query.expression.ParameterExpression

the Method:

public List<Appointment> getAppointments(User user)
 {
 PersistenceManager pm = PMF.get().getPersistenceManager();
 Query q = pm.newQuery(Appointment.class);
 q.setFilter("userPara == createdBy");
 q.declareParameters("String userPara");
 List<Appointment> queryResult = (List<Appointment>) q.execute(user.getUserId());
 return queryResult;
 }

The important part of the object

@PersistenceCapable(detachable = "true")

public class Appointment implements javax.jdo.listener.StoreCallback

{

@PrimaryKey

@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)

private Long id;
@Persistent

private String createdBy; //contains the userid

...
}

How can I declare the Parameter correct? 

Have a nice day

Benjamin