Issue
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
Solution
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
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
Answered By - Roel Strolenberg