JPA投影：只选择@OneTomany关系的部分项目和整个实体

Question

我有这两个实体：

@Entity
@Table(name = "ORGANIZATION")
public class Organization implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @OneToMany(mappedBy = "organization", fetch = FetchType.LAZY)
    private Set<OrganizationMeta> metas;

    public Organization() {
        super();
    }

    public Organization(Long id, String name, Set<OrganizationMeta> metas) {
        super();
        this.id = id;
        this.name = name;
        this.metas = metas;
    }

    // ... others fields ... getters and setters
}

@Entity
@Table(name = "ORGANIZATION_META")
public class OrganizationMeta implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Enumerated(EnumType.STRING)
    @Column(name = "meta_key", length = 200, nullable = false)
    private OrganizationMetaKeyEnum metaKey;

    private String metaValue;

    @ManyToOne(optional = false, fetch = FetchType.LAZY)
    @JoinColumn(nullable = false)
    private Organization organization;

    // ... getters and setters ...
}

所以一个组织可以有一个或多个OrganizationMeta，这是一个简单的情况。

@Query("select new net.feed.feedentity.domain.organization.Organization(organization.id, organization.name, organization.metas) from Organization organization left join fetch organization.metas where organization.id = ?1")

有可能做到这一点吗？有人遇到过这个问题吗？

Answer 1

我建议您通过使用Organization实体进行封闭投影技术来接收数据，因为您需要的只是Organization类的一个子集。

在这种情况下；您需要定义一个投影接口，它需要包含您感兴趣的属性的getter方法。那是你必须遵守的规则。名称应该匹配。

界面将如下所示：

public interface OrganizationView {
    String getId();
    String getName();
    Set<OrganizationMeta> getMetas();
}

public interface OrganizationRepository extends JpaRepository<Organization, Long> {

    @Query("select organization.id, organization.name, organization.metas from Organization organization left join fetch organization.metas where organization.id = ?1")
    List<OrganizationView> findSubsetById(Long id);
}

编辑：你可以看一看这个页面关于投影的解释与样本。