I need to create an object using an object id from a MySQL database

Question

I'm developing an inventory management system and I'm working on the final part of allowing users to update orders. This update requires items to be added or removed from the order. I'm working on adding the part now. I've tested the MySQL query that works in Workbench:

INSERT INTO order_items (item_quantity, fk_item_id, fk_order_id) VALUES (1,  (SELECT item_id FROM items WHERE item_id= 1), (SELECT order_id FROM orders WHERE order_id=2));

In Java, I know that I need to create an Item object based on the ID passed in above. This is OrderDAO:

public Order addItem(Order order) {
        ItemDAO itemDao = new ItemDAO();
        try (Connection connection = DBUtils.getInstance().getConnection();
                PreparedStatement statement = connection.prepareStatement("INSERT INTO order_items (item_quantity, fk_item_id, fk_order_id) VALUES (?,  (SELECT item_id FROM items WHERE item_id = ?), (SELECT order_id FROM orders WHERE order_id = ?));");) {
            statement.setInt(1, order.getItemQuantity());
            statement.setLong(2, order.getItemId());
            itemDao.read(order.getItemId());
            statement.setLong(3, order.getOrderId());
            statement.executeUpdate();
            System.out.println(order);
            return read(order.getOrderId());
        }  catch (Exception e) {
            LOGGER.debug(e);
            LOGGER.error(e.getMessage());
        }
        return null;
    }

This is the controller:

@Override
    public Order update() {
        LOGGER.info("Please enter the id of the order you would like to update");
        Long id = utils.getLong();
//      LOGGER.info("Would you like to add or delete an item from an order");
        LOGGER.info("Please enter the ID of the item you wish to add");
        Long itemId = utils.getLong();
        LOGGER.info("Please enter the quantity of the item to add");
        int quantity = utils.getInt();
        Item item = new Item(itemId);
        System.out.println(item);
        Order order = orderDAO.addItem(new Order(item, quantity, id));
        LOGGER.info("Order Updated\n");
        return order;
    }

I saw something similar here but not quite sure how to adapt it. I know I'm about to drop a price because I'm considering using the ItemDAO.read(Long id) method in the ItemDAO class, but I don't know how to set the properties of the Item object using that method.

New to the DAO model and JDBC so if there is already an answer I can't find it so I would be grateful if I could point me in the right direction.

edit: This is the ItemDAO read() method and the modelFromResults() method:

@Override
    public Item read(Long id) {
        try (Connection connection = DBUtils.getInstance().getConnection();
                PreparedStatement statement = connection.prepareStatement("SELECT * FROM items WHERE item_id = ?");) {
            statement.setLong(1, id);
            try (ResultSet resultSet = statement.executeQuery();) {
                resultSet.next();
                return modelFromResultSet(resultSet);
            }
        } catch (Exception e) {
            LOGGER.debug(e);
            LOGGER.error(e.getMessage());
        }
        return null;

@Override
    public Item modelFromResultSet(ResultSet resultSet) throws SQLException {
        Long itemID = resultSet.getLong("item_id");
        String itemName = resultSet.getString("item_name");
        double itemCost = resultSet.getDouble("item_cost");
        return new Item(itemID, itemName, itemCost);
    }

Answer 1

solution:

OrderDAO：

public Order orderItemsFromResultSet(ResultSet rs) throws SQLException {
        Long orderId = rs.getLong("order_items_id");
        Long itemId = rs.getLong("item_id");
        String itemName = rs.getString("item_name");
        double itemCost = rs.getDouble("item_cost");
        Item item = new Item(itemId, itemName, itemCost);
        Order order = new Order(item, orderId);
        return order;
    }
    @Override
    public Order read(Long id) {
        try (Connection connection = DBUtils.getInstance().getConnection();
                PreparedStatement statement = connection.prepareStatement("SELECT * FROM order_items LEFT OUTER JOIN items ON items.item_id = order_items.fk_item_id WHERE fk_order_id = ?;");) {
            statement.setLong(1, id);
            try (ResultSet resultSet = statement.executeQuery();) {
                resultSet.next();
                return orderItemsFromResultSet(resultSet);
            }
        } catch (Exception e) {
            LOGGER.debug(e);
            LOGGER.error(e.getMessage());
        }
        return null;
    }
public Order addItem(Order order) {
        
        try (Connection connection = DBUtils.getInstance().getConnection();
                PreparedStatement statement = connection.prepareStatement("INSERT INTO order_items (item_quantity, fk_item_id, fk_order_id) VALUES (?,  (SELECT item_id FROM items WHERE item_id = ?), (SELECT order_id FROM orders WHERE order_id = ?));");) {
            statement.setInt(1, order.getItemQuantity());
            statement.setLong(2, order.getItemId());
            statement.setLong(3, order.getOrderId());
            statement.executeUpdate();
            return read(order.getOrderId());
        }  catch (Exception e) {
            LOGGER.debug(e);
            LOGGER.error(e.getMessage());
        }
        return null;
    }
public Order removeItem(Order order) {
        try (Connection connection = DBUtils.getInstance().getConnection();
                PreparedStatement statementOne = connection.prepareStatement("UPDATE order_items SET item_quantity = item_quantity - 1 WHERE item_quantity >= 0 && fk_item_id = ? && fk_order_id = ?");
                PreparedStatement statementTwo = connection.prepareStatement("DELETE FROM order_items WHERE item_quantity = 0");) {
            statementOne.setLong(1, order.getItemId());
            statementOne.setLong(2, order.getOrderId());
            statementOne.executeUpdate();
            statementTwo.executeUpdate();
        }  catch (Exception e) {
            LOGGER.debug(e);
            LOGGER.error(e.getMessage());
        }
        return null;
    }

Order Controller:

@Override
    public Order update() {
        LOGGER.info("Please enter the id of the order you would like to update");
        Long id = utils.getLong();
        LOGGER.info("Would you like to add or delete an item from an order");
        String addOrDelete = utils.getString();
        addOrDelete = addOrDelete.toLowerCase();
        if (addOrDelete.equals("add")) {
            LOGGER.info("Please enter the ID of the item you wish to add");
            Long itemId = utils.getLong();
            LOGGER.info("Please enter the quantity of the item to add");
            int quantity = utils.getInt();
            Item item = new Item(itemId);
            ItemDAO itemDao = new ItemDAO();
            item = itemDao.read(item.getItemID());
            Order order = orderDAO.addItem(new Order(item.getItemID(), quantity, id));
            LOGGER.info("Order Updated\n");
            return order;
        } 
        else if (addOrDelete.equals("delete")) {
            LOGGER.info("Please enter the id of the item you wish to remove");
            Long itemId = utils.getLong();
            Order order = new Order();
            order.setOrderId(id);
            order.setItemId(itemId);
            orderDAO.removeItem(order);
            LOGGER.info("Order Updated\n");
            return order;
        }
        return null;
    }

It has full functionality to add items and delete items, as well as delete any order with a quantity of 0 items.