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;

 }

它的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：

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();

这个问题是它只返回country不为null的用户，因为生成的查询包含：inner join Country on User.country=Country.id 其中必须加入。

我该如何解决这个问题？

Answer 1

您可以尝试通过添加联接来强制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，这个问题可能在其他地方，因为我无法在我的环境中重新产生这个问题。

在JPA中使用空值连接列

1 个答案: