jpa-hibernatelisted

# JPA + Hibernate ## Quick start ```java @Entity @Table(name = "users") @Getter @Setter @NoArgsConstructor @AllArgsConstructor public class User { @Id @GeneratedValue(strategy = GenerationType.UUID) private UUID id; @Column(nullable = false, unique = true) private String email; @Column(nullable = false) private String name; @Version private Long version; } @Repository public interface UserRepository extends JpaRepository<User, UUID> { Optional<User> findByEmail(String email); boolean existsByEmail(String email); @EntityGraph(attributePaths = {"orders"}) @Query("SELECT u FROM User u WHERE u.id = :id") Optional<User> findByIdWithOrders(@Param("id") UUID id); } ``` Detailed patterns: `references/entity-mapping.md`, `references/fetch-strategies.md`, `references/transactional-semantics.md`, `references/projection.md`. ## Assets - `assets/templates/Entity.java.tmpl` - `assets/templates/Repository.java.tmpl` ## Hard rules - ALWAYS `FetchType.LAZY` for collections (`@OneToMany`, `@ManyToMany`). - ALWAYS use `JOIN FETCH` or `@EntityGraph` in queries that need collection eagerly. - NEVER access lazy collection outside `@Transactional` boundary (LazyInitializationException). - ALWAYS `@Version` for optimistic locking on entities with concurrent writes. - USE `Optional<T>` for `findOne/findById` returns, never `null`. ## Exit criteria - [ ] Entity has `@Version` field if updates expected concurrently - [ ] Collections