Spring Data JPA 映射VO/DTO对象方式

Spring Data JPA 映射VO/DTO对象

在项目开发中,时常需要根据业务需求来映射VO/DTO对象(这两个概念理解感觉很模糊- 。- )，本文将简单介绍以Spring Data JPA的方式处理实体类映射

HQL方式

public interface MusicTypeRepository extends JpaRepository<MusicType,Integer> {
    @Query("select new cn.srblog.springbootcurd.vo.StudentTypeInfoVo(count(s.id),m.name) " +
            "FROM MusicType m  left JOIN Student s on s.musicTypeId = m.id group by m.id ")
    List<StudentTypeInfoVo> getTypeInfo();
}

• 填写实体类路径,构造参数顺序要一致,字段名一律为实体类中的属性

• 如果配置了实体类属性的映射关系，则on s.musicTypeId = m.id语句可以省略

VO实体类

@Value
public class StudentTypeInfoVo  {
   private Long count;
   private String name;
}

使用Lombok的 @Value 注解

• 默认生成带参构造方法

• 默认为成员变量添加final修饰,且只提供getter()方法

原生SQL的形式

接口形式

public interface CoursePlanRepository extends JpaRepository<CoursePlan,Integer> {
      @Query(nativeQuery = true,value = "SELECT " +
              " c.id as id," +
              "DAYOFWEEK(c.start_time) as week," +
              "m.name as musicType," +
              "t.name as teacherName," +
              "c.start_time as startTime," +
              "c.end_time as endTime " +
              " FROM t_courseplan c,t_musictype m , t_teacher t " +
              " WHERE DATE(c.start_time) < DATE_ADD(CURDATE(), INTERVAL 7 DAY ) AND CURDATE() <= DATE(c.start_time) " +
              " and t.id=c.tea_id and c.music_type_id = m.id order by c.start_time ")
      List<CoursePlanVos> getWeekList();
}

• nativeQuery = true 表示开启原生SQL查询

• 查询字段别名需要与实体类中字段一一对应

• 该方 * 能为查询一周后的数据

VO实体类(接口形式)

public interface CoursePlanVos{
   Integer getId();
   Integer getWeek();
   String getMusicType();
   String getTeacherName();
   Date getStartTime() ;
   Date getEndTime();
}

结果集形式

@Query(value = "select count(s.id) as count,m.name as name " +
            " FROM t_musictype m  left JOIN t_student s on s.music_type_id = m.id group by m.id ",nativeQuery = true)
   List<Object[]> listType1();

对比第一种方法,使用原生SQL默认会返回Object数组

Spring Data Jpa 自定义repository转DTO

近期项目中需要 关联 几张表再把字段转出来，在这里记录以下，我感觉网上写的都不太规范和清晰。

@Entity
@SqlResultSetMapping(
       name="TestMapping",
       entities = {
               @EntityResult(
                       entityClass = com.xxx.xx.data.model.TestEntity.class,
                       fields = {
                               @FieldResult(name="id",column="id"),
                               @FieldResult(name="localTime",column="time"),
                               @FieldResult(name="maximumAppointment",column="maxAppointment"),
                       }
               )
       }
)
@NamedNativeQuery(name="getTestQuery",
       query="select tableC.id as id,tableB.time,tableC.maximumAppointment as maxAppointment from tableB " +
               "                              inner join tableA on tableA.id = tableB.tableAId " +
               "                              inner join tableC on tableB.id = tableC.tableBId " +
               "                              inner join custom on custom.id = tableA.customId " +
               "where " +
               "   tableA.locationId = :locationId" +
               "   and custom.id = :customId" +
               "   and tableB.deleted = false ", resultSetMapping="TestMapping")
@Data
public class TestEntity {
   @Id
   private String id;
   private LocalTime localTime;
   private Integer maximumAppointment;
}

需要声明接口：

@Repository
public interface TestEntityRepository extends JpaRepository<TestEntity,String> {
   @Query(name="getTestQuery")
   List<TestEntity> getTestQuery(String locationId, String customId);
}

若不想声明接口，那可以用EntityManager 来实现。

CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();

来源：https://blog.csdn.net/qq_20122925/article/details/90179756