Java.Hibernate.Middle.What is the @Version annotation for?

🔎 Detailed Explanation

🔹 How it works

• When you annotate a field with @Version, Hibernate automatically:
  ✅ Reads the version value when loading the entity.
  ✅ Checks the version when updating → if the version in the database doesn’t match the version your entity has, Hibernate throws an OptimisticLockException.
  ✅ Increments the version value after a successful update.

Typical types for @Version fields:

• int / Integer → incremented by 1 each update.
• long / Long → incremented by 1.
• java.sql.Timestamp → updated with the current timestamp on each update.

🔹 Example

@Entity
public class Product {
    @Id
    private Long id;

    private String name;
    private double price;

    @Version
    private int version; // automatically managed by Hibernate
}

🔹 What happens on update?

• Suppose you load a Product with version=5.
• If another transaction updates it and increments the version to 6 before you commit:
  • When you try to update, Hibernate detects a mismatch (5 vs 6) and throws:

javax.persistence.OptimisticLockException: Row was updated or deleted by another transaction

✅ This prevents lost updates, where concurrent transactions overwrite each other’s changes silently.

🔹 Optimistic vs. Pessimistic locking

• Optimistic (with @Version): no database locks → best for low-contention systems.
• Pessimistic (with explicit locks): database locks to block concurrent modifications.

📊 Benefits of @Version

✅ Protects your data from concurrent updates.
✅ Lightweight → no need for DB locks → better scalability.
✅ Automatic version management by Hibernate.

📌 Key Takeaways

✅ Annotate an entity field with @Version to enable optimistic locking.
✅ Hibernate uses the version to detect concurrent modifications → avoiding lost updates.
✅ Best for high-read, low-conflict systems needing safe concurrent updates.