Combo Specific HowTos

How can I populate combo with data from db?

To define options of combo you should use ComboConnector on the server side and specify the connector file in the load() method on the client side:

client side:

var combo=new dhtmlXCombo("combo_zone2","alfa2",200);
combo.load("http://localhost:8080/connector");

server side:

public class DataBaseConnection {
 Connection getConnection(){
  Connection conn=null;
  try {
   Class.forName ("com.mysql.jdbc.Driver").newInstance ();
   conn = DriverManager.getConnection(
        "jdbc:mysql://localhost/sampledb?characterEncodingTF-8", 
        "root", 
        ""
    );
  } catch (Throwable e) {
   e.printStackTrace();
  }
  return conn;
 }
}

and

import com.dhtmlx.connector.ConnectorServlet;
import com.dhtmlx.connector.DBType;
import com.dhtmlx.connector.ComboConnector;
 
import java.sql.Connection;
 
public class AppServer extends ConnectorServlet {
 
 /**
  * 
   */
 private static final long serialVersionUID = 1L;
 
 /* (non-Javadoc)
 
 * @see com.dhtmlx.connector.ConnectorServlet#configure()
 */
 
@Override
protected void configure() {
    Connection conn = ( new DataBaseConnection()).getConnection();
    СomboConnector data = new ComboConnector(conn);
    data.render_table("categories","id","valueColumn, labelColumn");
 }
}

Names of the fields can have aliases (value or label) to identify the appropriate attribute.

data.render_sql(
    "SELECT *, CONCAT(FirstName, LastName) as label FROM table1",
    "id",
    "id,FirstName(label)"
);

Note, in the filtering mode Combo filters data by the "label" field.