Kepiye carane Spring Data JPA mlaku lan apa iku derived query?

Question

IT Interview Practice · Accepted Answer

Spring Data JPA ngilangi boilerplate nulis kelas DAO. Kowe ndeklarasi **interface** repository; nalika wiwitan Spring ngasilake implementasi proxy sing didhukung JPA/Hibernate. Kowe ora tau nulis `entityManager.persist(...)` kanggo CRUD dhasar. ## Entitas + repository ```java @Entity public class User { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String email; private boolean active; // getters/setters } // Extend JpaRepository to inherit save/findById/findAll/delete. public interface UserRepository extends JpaRepository { // Derived query: Spring parses the METHOD NAME into a WHERE clause. // -> SELECT * FROM user WHERE email = ? AND active = true Optional findByEmailAndActiveTrue(String email); // Keywords compose: OrderBy, Between, Containing, In, LessThan... List findByActiveTrueOrderByEmailAsc(); } ``` ## Derived vs @Query Derived query bisa diwaca kanggo kriteria prasaja nanging njeblug dawa nalika kondisi tambah. Nalika kuwi kedadeyan, mudhun menyang `@Query` eksplisit: ```java @Query("SELECT u FROM User u WHERE u.email = :email") // JPQL, not SQL Optional lookup(@Param("email") String email); // Native SQL when you need DB-specific features: @Query(value = "SELECT * FROM users WHERE active = true", nativeQuery = true) List findActiveNative(); ``` ## Paging teka kanthi gratis ```java Page findByActiveTrue(Pageable pageable); // pass PageRequest.of(0, 20) ``` ## Kenapa iki penting Pewawancara nyelidiki apa kowe ngerti apa sing digawe *ing mburi* interface. Sinyal sing kuat: ngerti kata kunci derived-query, milih `@Query` nalika jeneng metode dadi ngrepoti, nganggo `Pageable` tinimbang ngemot kabeh tabel, lan ngerti yen asosiasi lazy bisa micu **masalah N+1** — topik sing kerep dijorogake menyang pitakon sabanjure.

Entitas + repository

Derived vs @Query

Paging teka kanthi gratis

Kenapa iki penting

Pitakon sing gegandhengan