JAVA JDBC：为 ID 列生成的键在表记录中返回 null

Question

I am new to Java and above all to Java JDBC. I am trying to develop a simple DAO-Implementation for a GUI, in which fields from a panel get filled out and the datas get stored in an Oracle DB table named EventList. At the moment it works with all the field of the class Event (Model) with the exception of the EventID column. I am trying to generate an auto-increment integer through the statement GENERATED KEYS but, even though I tried different ways to reorganize the "INSERT" query in the method saveData2(), the record remains null and no keys are generated. What I am doing wrong? Every hint would be really appreciated!

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

public class EventDAOImpl implements EventDAO {

    @Override
    public void saveData2(Event event) {
        OracleDsSingleton ora =   OracleDsSingleton.getInstance();
        int primKey = 0;
        try {
            Connection connection = ora.getConnection();
            String addQuery = "INSERT INTO EventList(EventName, EventPlace, EventDate, EventDescription, EventCategory) VALUES (?,?,?,?,?)";
            //PreparedStatement ptmt = connection.prepareStatement(addQuery, Statement.RETURN_GENERATED_KEYS); 
//          ResultSet generatedKey = ptmt.getGeneratedKeys();
//                      if (generatedKey.next()) {
//              int key = generatedKey.getInt(1);
//              System.out.println(key);
//            }
            String columnNames [] = new String [] {"EventId"};
            
            PreparedStatement ptmt = connection.prepareStatement(addQuery, columnNames);
            
            ptmt.setString(1, event.getName());
            ptmt.setString(2, event.getPlace());
            ptmt.setString(3, event.getDate());
            ptmt.setString(4, event.getDescription());
            ptmt.setString(5, event.getCategory());
            
            //ptmt.executeUpdate();
                        
            if(ptmt.executeUpdate() > 0) {
                java.sql.ResultSet generatedKey = ptmt.getGeneratedKeys();
                if (generatedKey.next() ) {
                    event.setEventID(generatedKey.getInt(1));
                }
            }
            System.out.println("Data successfully added!");
            //System.out.println("Table updated with EventID = " + primKey);
            System.out.println(event.getName());
            
            
        } catch (SQLException e) {
            e.printStackTrace();
        }
        
    }
}

Answer 1

Most things in the JDBC standard are optional. DBs are free to return nothing for .getGeneratedKeys() . Even when you ask for them. But you didn't, so, there's hope!

Try con.prepareStatement("SQL HERE", Statement.RETURN_GENERATED_KEYS) first. But, if that doesn't work, you're in for a lot more effort. Run a query to fetch the next value from the sequence (and figuring out the name of that sequence in order to do this can be quite a job,). then insert that explicitly. Let's hope it doesn't need to come to this.

NB: Modern DB design generally ditches the concept of an auto-count ID because keeping that counter 'in sync' with replicated servers and all that jazz is a giant headache. If you're still at the beginning phases of all this, why not follow modern conventions? Make the ID a UUID, and just let java generate it. They are no longer consecutive values, instead, they are long randomly generated strings (and with enough bits that even trillions if inserts still have less chance of a collision than you winning the lottery without buying a ticket whilst getting struck by 2 separate meteors, and lightning, all at once).