Include rownum in toplink

Question

When we form the query using Expression in toplink. How we can add rownum as one of the field in the query??

Answer 1

To use ROWNUM for pagination in 10.1.3.3 you will need to extend the framework. Below is a QueryRedirector that can be used with any read query to translate the firstResult and maxRow configurations into Oracle specific ROWNUM SQL.
package oracle.toplink.extension.queryframework;
import oracle.toplink.internal.databaseaccess.DatasourceCall;
import oracle.toplink.internal.sessions.AbstractSession;
import oracle.toplink.publicinterface.DatabaseRow;
import oracle.toplink.queryframework.*;
import oracle.toplink.sessions.Record;
import oracle.toplink.sessions.Session;
* This is an example of how a TopLink QueryRedirector can be used to extend the
* query framework and provide Oracle specific ROWNUM filtering. The redirector
* forces the generation of the SQL for the query and wraps it in additional
* SQL clauses to limit the results being returned.
* http://www.oracle.com/technology/oramag/oracle/06-sep/o56asktom.html
* Limitations/Issues:
* - Code provided as is for 10.1.3.3. The complete feature has been added to
*   Oracle TopLink 11gR1 and EclipseLink
* - Does not support limiting the rows on batch reading of relationships
* @author Doug Clarke
* @since Oracle TopLink 10.1.3.3
public class OracleRowNumRedirector implements QueryRedirector {
    public static final String PREFIX =
        "SELECT * FROM ( SELECT a.*, ROWNUM rnum FROM (";
    public static final String MAX_COMPARE = ") a WHERE ROWNUM <= "; // MAX
    public static final String MIN_COMPARE = ")  WHERE rnum  >= "; // FIRST
    public Object invokeQuery(DatabaseQuery query, Record arguments,
                              Session session) {
        AbstractSession sessionImpl = (AbstractSession)session;
        DatabaseRow argsImpl = (DatabaseRow)arguments;
        // Ensure the query is read and the max value is set
        if (query.isReadQuery() && ((ReadQuery)query).getMaxRows() > 0) {
            query.checkPrepare(sessionImpl, argsImpl);
            SQLCall call = (SQLCall)query.getCall();
            ReadQuery readQuery = (ReadQuery)query;
            boolean usesBinding = call.usesBinding(sessionImpl);
            // Cache the values
            int maxValue = readQuery.getMaxRows();
            int firstValue = readQuery.getFirstResult();
            // Compute the string values for the SQL creation
            String max = usesBinding ? "?" : Integer.toString(maxValue);
            String first = usesBinding ? "?" : Integer.toString(firstValue);
            // Provide the custom SQL and reset the call so the query does not generate its own SQL
            call.setSQLString(PREFIX + call.getSQLString() + MAX_COMPARE +
                              max + MIN_COMPARE + first);
            query.setCall(call);
            // Clear the previous first & max values to ensure the JDBC limits are
            // not applied
            readQuery.setFirstResult(0);
            readQuery.setMaxRows(0);
            call.setFirstResult(0);
            call.setMaxRows(0);
            // If binding is enabled then add the values to the call's parameters
            if (usesBinding) {
                call.getParameters().add(maxValue);
                call.getParameterTypes().add(DatasourceCall.LITERAL);
                call.getParameters().add(firstValue);
                call.getParameterTypes().add(DatasourceCall.LITERAL);
        // Continue the execution with the query as is
        return query.execute(sessionImpl, argsImpl);
}To use it you simply need to configure the redirector on your query prior to execution:
        ReadAllQuery raq = new ReadAllQuery(Employee.class);
        raq.addAscendingOrdering("id");
        raq.setFirstResult(6);
        raq.setMaxRows(10);
        raq.setRedirector(new OracleRowNumRedirector());Doug