如何使用自定義 Dto 查詢從 mysql 表的列中獲取 JSON 字符串列表

Question

我想使用 dto 從表的特定列查詢列表，我的實際查詢非常復雜，包含 3 個連接，我為問題陳述添加了虛擬代碼。

我正面臨這個錯誤：

org.springframework.dao.InvalidDataAccessApiUsageException：無法在 class 上找到合適的構造函數：com.example.demo.persistence.mysql.dto.StudentDto； 嵌套異常是 java.lang.IllegalArgumentException: Could not locate appropriate constructor on class: com.example.demo.persistence.mysql.dto.StudentDto

Students.java

@SqlResultSetMapping(name = "StudentMapping", classes = {
        @ConstructorResult(targetClass = StudentDto.class, columns = {
                @ColumnResult(name = "friendList", type = List.class)})})

@Data
@Table(name = "student")
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false)
    private Long id;

    @Column(name = "name", nullable = false, length = 100)
    private String name;

    @Type(type = "json")
    @Column(name = "friend_list", columnDefinition = "json")
    @Builder.Default
    private List<String> friendsName = new ArrayList<>();
}

StudentDto.java

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class StudentDto implements Serializable {

    @Type(type = "json")
    @Column(name = "friend_list", columnDefinition = "json")
    List<String> friends;
}

StudentsCustomRepository.java

public StudentsDto fetchStudentFriends(Long id) {
        String rawQuery = String.format(
                "select friend_list as friends from student where id = '%s';",
                id);
        Query query = entityManager.createNativeQuery(rawQuery, "StudentMapping");
        return (StudentDto) query.getResultList();
    }

Answer 1

如果您想直接從數據庫導入為 dto object，則可以使用自定義查詢。

例如 -> @Query("SELECT new com.demo.dtos.userInfoDTO(user.id, user.username) FROM User user")