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package org.apache.cayenne.dba.derby;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Collections;

import org.apache.cayenne.CayenneException;
import org.apache.cayenne.access.DataNode;
import org.apache.cayenne.access.QueryLogger;
import org.apache.cayenne.dba.JdbcPkGenerator;
import org.apache.cayenne.map.DbEntity;

/**
 * Default PK generator for Derby that uses updateable ResultSet to get the next id from
 * the lookup table.
 * 
 * @since 1.2
 * @author Andrus Adamchik
 */
public class DerbyPkGenerator extends JdbcPkGenerator {

    static final String SELECT_QUERY = "SELECT NEXT_ID FROM AUTO_PK_SUPPORT"
            + " WHERE TABLE_NAME = ? FOR UPDATE";

    protected int pkFromDatabase(DataNode node, DbEntity entity) throws Exception {

        if (QueryLogger.isLoggable()) {
            QueryLogger.logQuery(SELECT_QUERY, Collections
                    .singletonList(entity.getName()));
        }

        Connection c = node.getDataSource().getConnection();

        try {
            PreparedStatement select = c.prepareStatement(
                    SELECT_QUERY,
                    ResultSet.TYPE_FORWARD_ONLY,
                    ResultSet.CONCUR_UPDATABLE);

            select.setString(1, entity.getName());
            ResultSet rs = select.executeQuery();

            if (!rs.next()) {
                throw new CayenneException("PK lookup failed for table: "
                        + entity.getName());
            }

            int nextId = rs.getInt(1);

            rs.updateInt(1, nextId + pkCacheSize);
            rs.updateRow();

            if (rs.next()) {
                throw new CayenneException("More than one PK record for table: "
                        + entity.getName());
            }
            
            rs.close();

            select.close();
            c.commit();

            return nextId;
        }
        finally {
            c.close();
        }
    }
}