java - 在 JPA 中加入具有空值的列

Question

我有一个实体如下:

public class User {

    @Id
    @Column
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "idgenx_gx")
    private Long id;

    @Column
    private String name;

    @Column
    private String lastname;

    @ManyToOne(fetch = FetchType.LAZY, optional = true)
    private Country country;

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

 }

它是 dto:

public class UserDTO {

    private Long id;
    private String name;
    private String lastname;
    private String organizationName;
    private Country country;

}

使用 JPA Criteria API 我想从数据库中选择所有用户，所以我做了如下操作:

final CriteriaBuilder builder = getCriteriaBuilder();
final CriteriaQuery<UserDTO> query = builder.createQuery(UserDTO.class);
final Root<User> from = query.from(User.class);
Join<User, Organization> joinOrg = from.join(User_.organization, JoinType.LEFT);
query.multiselect(from.get(User_.id), from.get(User_.name), from.get(User_.lastname),
                 joinOrg.get(Organization_.name), from.get(User_.country));
query.distinct(true);

return getEntityManager().createQuery(query).getResultList();

这个问题是它将只返回国家不为空的用户，因为生成的查询包含这个:inner join Country on User.country=Country.id必须保留 join 代替。

我该如何解决这个问题？

Answer 1

您也可以尝试通过添加连接来强制 JoinType.LEFT，例如:

Join<User, Country> joinCountry = from.join("country", JoinType.LEFT);   
query.multiselect(from.get("id"), from.get("name"), from.get("lastname")
                              ,joinOrg.get("name"), joinCountry );

无论如何，这个问题可能出在其他地方，因为我无法在我的环境中重现它。