What are the main differences between using Spring Data JPA and Spring Data JDBC when working with databases?.

Main differences between Spring Data JPA and Spring Data JDBC:

• Level of abstraction: Spring Data JPA works on top of JPA (Hibernate, etc.) and supports ORM with full management of entities and relationships. Spring Data JDBC is more lightweight, works directly with SQL, without complex ORM.

• Handling relationships: JPA supports lazy loading, cascading operations, complex relationships (OneToMany, ManyToMany). JDBC only supports simple relationships, without lazy loading and cascades.

• Performance: Spring Data JDBC is usually faster and simpler, as it has less overhead, but requires more manual management.

• Complexity and flexibility: JPA is suitable for complex models with many relationships and business logic. JDBC is for simple models and cases where high performance and control are needed.

Example of using Spring Data JPA:

@Entity
public class User {
    @Id
    private Long id;
    private String name;
    @OneToMany(mappedBy = "user")
    private List<Order> orders;
}

In Spring Data JDBC, such relationships need to be implemented manually.