How to fetch only selected attributes of an entity using Spring JPA?

Question

I'm using Spring Boot (1.3.3.RELEASE) and Hibernate JPA in my project. My entity looks like this:

@Data @NoArgsConstructor @Entity @Table(name = "rule") public class RuleVO {      @Id     @GeneratedValue     private Long id;      @Column(name = "name", length = 128, nullable = false, unique = true)     private String name;      @Column(name = "tag", length = 256)     private String tag;      @OneToMany(mappedBy = "rule", cascade = CascadeType.ALL, orphanRemoval = true)     private List<RuleOutputArticleVO> outputArticles;      @OneToMany(mappedBy = "rule", cascade = CascadeType.ALL, orphanRemoval = true)     private List<RuleInputArticleVO> inputArticles; } 

My repository looks like this:

@Repository public interface RuleRepository extends JpaRepository<RuleVO, Long> { } 

In some cases I need to fetch only id and name attributes of entity RuleVO. How can I achieve this? I found a notice it should be doable using Criteria API and Projections but how? Many thanks in advance. Vojtech

Answer 1

UPDATE:

As has been pointed out to me, I'm lazy and this can very well be done hence I'm updating my answer after having looked around the web for a proper one.

Here's an example of how to get only the id's and only the names:

@Repository public interface RuleRepository extends JpaRepository<RuleVO, Long> {      @Query("SELECT r.id FROM RuleVo r where r.name = :name")      List<Long> findIdByName(@Param("name") String name);      @Query("SELECT r.name FROM RuleVo r where r.id = :id")      String findNameById(@Param("id") Long id); } 

Hopefully this update proves helpful

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Old Answer:

Only retrieving the specific attributes name/id is not possible as this is not how spring was designed or any SQL database for that matter as you always select a row which is an entity.

What you CAN do is query over the variables in the entity, for instance:

@Repository public interface RuleRepository extends JpaRepository<RuleVO, Long> {      public RuleVo findOneByName(String name);     public RuleVo findOneByNameOrId(String name, Long id);     public List<RuleVo> findAllByName(String name);     // etc, depending on what you want } 

You can modify these however you want w.r.t. your needs. You can call these methods directly via the autowired repository

See http://docs.spring.io/spring-data/jpa/docs/current/reference/html/ Section 5.3 for more options and examples