使用简单实体映射数据库视图实体，并使用Spring Data传递给DTO

Question

我只是在学习Spring Data。 我想用一个简单的Entity映射数据库视图Entity并传​​递给DTO，DTO将同时包含两个实体的列。 我知道我可以使用特殊的数据库视图，但是我需要精确地映射Spring Data的实体。 我有一个数据库视图实体“ MentorStudents”：

@Entity
@Table(name = "mentor_students")
@Immutable
public class MentorStudents implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "mentor_id", updatable = false, nullable = false)
    private Long mentorId;

    //This entity I need to map
    private Mentor mentor;

    @Column(name = "active_students")
    private Integer activeStudents;

    public MentorStudents() {
    }

    //getters, setters, equals, hashCode
}

上述实体的数据库视图sql是：

SELECT id AS mentor_id, active_students
   FROM mentor
LEFT JOIN ( SELECT mentor_id, count(mentor_id) AS active_students
   FROM contract
   WHERE close_type IS NULL
   GROUP BY mentor_id) active ON mentor.id = active.mentor_id
ORDER BY mentor.id;

我有一个简单的实体“ Mentor”：

@Entity
@Table(name = "mentor")
@Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
public class Mentor implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "sequenceGenerator")
    @SequenceGenerator(name = "sequenceGenerator")
    private Long id;

    @NotNull
    @Column(name = "first_name", nullable = false)
    private String firstName;

    @NotNull
    @Column(name = "last_name", nullable = false)
    private String lastName;

    @Column(name = "patronymic")
    private String patronymic;

    @Column(name = "phone")
    private String phone;

    @NotNull
    @Column(name = "email", nullable = false)
    private String email;

    @Column(name = "skype")
    private String skype;

    @Column(name = "country")
    private String country;

    @Column(name = "city")
    private String city;

    @Column(name = "max_students")
    private Long maxStudents;

    //getters, setters, equals, hashCode

我必须获得一个DTO，其中包含所有Mentor字段和一个不含“ mentorId”字段的“ activeStudents” MentorStudents字段。 怎么做

Answer 1

使用弹簧数据投影：

public interface YourDto {
  // all Mentor get fields
  String getFirstName();
  ...
  // activeStudents get field
  Integer getActiveStudents();
}

public interface YourRepository extends JpaRepository<YourEntity, Integer> {
  @Query(value = "select ...(all fields match YourDto) from Mentor m, MentorStudents s where m.id = s.mentorId and m.id = ?1")
  Optional<YourDto> findMyDto(Integer mentorId);
}