Update an existing entry with auto increment in Hibernate

Question

I have a class Price mapped to a db table using Hibernate. It's like this:

Price {
    long priceID; //auto increment, Primary key
    long itemID;  // Foreign key, each price corresponds to a unique Item
    double price; // actual price
}

What I want is when saving a price object with an existing itemID, it updates the price of the existing entry in db with the same itemID.

But it ended up creating a duplicate entry with the same itemID.

What can I do to avoid duplicate entry and update the existing entry?

Answer 1

You can implement something like below :

Introduce a method to check if Item is already exist in the DB:

// Session session= ...
public Map<Integer, Item> getItemIfExist(String item_name) {
    Map<Integer, Item> returnMap = new HashMap<>();
    Criteria cr = session.createCriteria(Item.class);
    cr.add(Restrictions.eq("itemName", item_name));
    List<Item> items = cr.list();
    for (Item item : items) {
        Set<Price> price = item.getPrices();
        for (Price p : price) {
            returnMap.put(p.getPriceId(), item);
        }
    }
    return returnMap;
}

If item is already in the DB you can update the price of the existing item:

    String item_name = "Water";//this may vary according to your requirement        
    double newPrice = 4.50;//as well as the price
    if (!checkItemIfExist(item_name).isEmpty()) {
        for (Map.Entry<Integer, Item> entry : checkItemIfExist(item_name).entrySet()) {
            int priceId = entry.getKey();
            Item item = entry.getValue();
            session.beginTransaction();
            Price price = (Price) session.load(Price.class, priceId);
            price.setItem(item);
            price.setPrice(newPrice);
            session.update(price);
            session.getTransaction().commit();

        }}

Else you can save it as an new item to the DB:

else {
        session.beginTransaction();
        Item item = new Item(item_name);
        Price price = new Price(item, newPrice);
        session.save(price);
        session.getTransaction().commit();
    }

Update :
Item Entity class :-

public class Item implements java.io.Serializable {

private Integer itemId;
private String itemName;
private Set<Price> prices = new HashSet<>();
...

Price Entity class :-

 public class Price  implements java.io.Serializable {

 private Integer priceId;
 private Item item;
 private double price;
 ...