Using Redirect Queries

A redirect query is a named query that delegates query execution control to your application. redirect queried allow you to define the query implementation in code as a static method.

To perform complex operations, you can combine query redirectors with the TopLink query framework.

Creating a Redirect Query

To perform complex operations, you can combine query redirectors with the TopLink query framework. To create a redirector, implement the oracle.toplink.queryframework.QueryRedirector interface. The query mechanism executes the Object invokeQuery(DatabaseQuery query, DatabaseRow arguments, Session session) method and waits for the results.

TopLink provides one preimplemented redirector, the MethodBasedQueryRedirector method. To use this redirector, create a static invoke method on a class, and use the setMethodName(String) call to specify the method to invoke.

Example 99-1 Redirect Query

ReadObjectQuery query = new ReadObjectQuery(Employee.class);
query.setName("findEmployeeByAnEmployee");
query.addArgument("employee");

MethodBaseQueryRedirector redirector = new
     MethodBaseQueryRedirector(QueryRedirectorTest.class, "findEmployeeByAnEmployee");
query.setRedirector(redirector);
Descriptor descriptor = getSession().getDescriptor(query.getReferenceClass());
descriptor.getQueryManager().addQuery(query.getName(), query);

Vector arguments = new Vector();
arguments.addElement(employee);
objectFromDatabase = getSession().executeQuery(query,arguments);

public class QueryRedirectorTest {
    public static Object findEmployeeByAnEmployee(
        DatabaseQuery query,
        oracle.toplink.publicinterface.DatabaseRow arguments,
        oracle.toplink.sessions.Session
        session) {
            ((ReadObjectQuery) query).setSelectionObject(arguments.get("employee"));
            return session.executeQuery(query);
    }
}