Bug 354572

Description darren 2011-08-11 21:44:13 EDT

Build Identifier: Eclipse Persistence Services - 2.2.0.v20110202-r8913

When TYPE is used on an identification variable in part of the result of a projection query with a constructor expression (only), I get the following exception (as applied to a searching on an example entity Employee extends Element, with a constructor expression ElementDTO(Class,Long,String): 

-Exception [EclipseLink-3007] (Eclipse Persistence Services - 2.2.0.v20110202-r8913): org.eclipse.persistence.exceptions.ConversionException
Exception in thread "main" Local Exception Stack: 
Exception Description: The object [Employee], of class [class java.lang.String], could not be converted to [class java.lang.Class].  Ensure that the class [Employee] is on the CLASSPATH.  You may need to use alternate API passing in the appropriate class loader as required, or setting it on the default ConversionManager
Internal Exception: java.lang.ClassNotFoundException: Employee

This happens whether or not I use application-managed or container-managed mode.

The problem is described with precise examples at: http://www.eclipse.org/forums/index.php/t/233012/

Reproducible: Always

Steps to Reproduce:
1. Create an entity class (such as Employee) that extends another entity class (such as Element), and ensure default single table ("super table) inheritance strategy is used, so DTYPE column will be generated. For the sake of this explanation, Element has fields 'id' and 'name' and Employee has additional field 'salary'.

2. Create a service that uses a projection query into a constructor expression such EmployeeDTO(Class entityClass, Long id, String name), where EmployeeDTO represents a transfer object to carry a minimal slice of a typically more complex Employee: 

    public List<EmployeeDTO> findAllEmployeeDTOs() {
        return em.createQuery(
        "SELECT NEW examples.model.EmployeeDTO(TYPE(e),e.id,e.name) "+
                "FROM Employee e "+ "ORDER BY e.name", EmployeeDTO.class).getResultList();        
    }

3.  Populate the database with some Employee objects, then run the projection query to trigger the error given above.

Please note that the projection query into Object[] (without a constructor expression) runs fine, and yields TYPE(e) as a 'class examples.model.Employee'. It is only when the projection query is fed into a constructor expression that the problem arises.

I've marked this as Major, since for my purposes this is a real show-stopper. It completely prevents my from migrating from full entity queries to minimalist projection queries in my application, since I definitely need to be able to expose in the user interface details of the entity class, and there is no other way of obtaining the information. So it prevents me from applying the project query strategy (a major feature) at all for my application.