Spring Data JPA — Entities & Repositories

Datenbankzugriff mit Spring Data JPA

Spring Data JPA eliminiert Boilerplate: Interfaces werden zu Queries.

Lektion 21: Entities

@Entity
@Table(name = "products")
public class Product {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @NotBlank private String name;
    @Positive private double price;
    // getter/setter/constructors
}

Lektion 22: Repositories

public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findByCategory(String category);
    List<Product> findByPriceLessThan(double price);
    Optional<Product> findByName(String name);
}

Spring Data generiert die Implementation zur Laufzeit — kein SQL schreiben.

Lektion 23: Query-Methoden & @Query

@Query("SELECT p FROM Product p WHERE p.price BETWEEN :min AND :max")
List<Product> findByPriceRange(@Param("min") double min, @Param("max") double max);

// Sortierung & Pagination
Page<Product> findAll(Pageable pageable);  // PageRequest.of(0, 20, Sort.by("price"))

Lektion 24: Relationships

@Entity
public class Order {
    @Id @GeneratedValue private Long id;
    @OneToMany(mappedBy = "order", cascade = CascadeType.ALL)
    private List<OrderItem> items = new ArrayList<>();
    @ManyToOne(fetch = FetchType.LAZY)
    private Customer customer;
}

Lektion 25: Pagination & Sorting

@GetMapping
public Page<Product> list(@RequestParam(defaultValue = "0") int page,
                          @RequestParam(defaultValue = "20") int size) {
    return repo.findAll(PageRequest.of(page, size, Sort.by("name")));
}