Have you used composite keys when working with Hibernate?

In Hibernate, composite keys are used to identify an entity using multiple fields instead of a single one. This is necessary when the unique identifier of an object is formed from a combination of several attributes.

To implement a composite key in Hibernate, a separate class is usually created, which implements Serializable and contains all the key fields. This class is used with the @Embeddable annotation or as @IdClass.

Example using @Embeddable:

@Embeddable
public class OrderItemId implements Serializable {
    private Long orderId;
    private Long productId;

    // constructors, equals, hashCode
}

@Entity
public class OrderItem {
    @EmbeddedId
    private OrderItemId id;

    private int quantity;
    // other fields and methods
}

Thus, Hibernate understands that the entity's identifier consists of multiple fields and works correctly with them during saving and searching.