前言

JPA支持使用@Query自定义查询，查询的结果需要字节用DTO对象接收，如果使用HQL的查询语句，可以将直接将DTO对象的构造方法传入hql中，直接转为DTO对象；而如果使用native sql查询的方式，只能将返回结果用Object[]对象接收，然后DTO设置对象的构造来接收Object[]里面的参数完成DTO对象的转换。

例子

mysql数据库表

用户表

  1. CREATE TABLE `pos_user` (
  2.   `id` bigint(20) NOT NULL AUTO_INCREMENT,
  3.   `user_name` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  4.   `user_pwd` varchar(255) DEFAULT NULL,
  5.   `user_type` int(11) DEFAULT NULL,
  6.   `parent_id` bigint(20) DEFAULT NULL,
  7.   `user_status` int(11) DEFAULT NULL,
  8.   `distributor_id` bigint(20) DEFAULT NULL,
  9.   `creator_identity_type` int(2) DEFAULT NULL,
  10.   `creator_id` bigint(20) DEFAULT NULL,
  11.   `create_date` varchar(50) DEFAULT NULL,
  12.   PRIMARY KEY (`id`)
  13. ) ENGINE=InnoDB AUTO_INCREMENT=22 DEFAULT CHARSET=utf8;

设备表

  1. CREATE TABLE `pos_device` (
  2.   `id` bigint(20) NOT NULL AUTO_INCREMENT,
  3.   `imei` varchar(120) NOT NULL,
  4.   `mac` varchar(120) NOT NULL,
  5.   `unique_code` varchar(120) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
  6.   `type` varchar(100) DEFAULT NULL,
  7.   `system_version` varchar(100) DEFAULT NULL,
  8.   `distributor_id` bigint(20) DEFAULT NULL,
  9.   `creator_identity_type` int(2) DEFAULT NULL,
  10.   `creator_id` bigint(20) DEFAULT NULL,
  11.   `create_date` varchar(50) DEFAULT NULL,
  12.   PRIMARY KEY (`id`)
  13. ) ENGINE=InnoDB AUTO_INCREMENT=31 DEFAULT CHARSET=utf8;

用户和设备关联表

  1. CREATE TABLE `pos_user_device_relation` (
  2.   `id` bigint(20) NOT NULL AUTO_INCREMENT,
  3.   `device_id` bigint(20) DEFAULT NULL,
  4.   `user_id` bigint(20) DEFAULT NULL,
  5.   PRIMARY KEY (`id`)
  6. ) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

可以看到用户和设备关联表中有用户id和设备id

联合查询的需求

想列出pos_user_device_relation表中所有pos_user的distributor_id=1的所有用户和设备，要求返回的信息包括用户的username、type信息和设备的imei、mac等信息。

sql语句

  1. SELECT
  2. pdr.id,
  3. pdr.device_id,
  4. pd.imei,
  5. pd.mac,
  6. pd.unique_code,
  7. pd.type,
  8. pd.system_version,
  9. pdr.user_id,
  10. pu.user_name,
  11. pu.user_type
  12. FROM
  13. pos_user_device_relation pdr, pos_user pu, pos_device pd
  14. WHERE pdr.device_id = pd.id AND pdr.user_id = pu.id AND pdr.user_id in (select id from pos_user where distributor_id=1) limit 0,10

查询可以正常得到结果，结果行是这样的：

  1. +----+-----------+---------------------+-------------------+--------------------------+----------+----------------+---------+---------------+-----------+
  2. | id | device_id | imei                | mac               | unique_code              | type     | system_version | user_id | user_name     | user_type |
  3. +----+-----------+---------------------+-------------------+--------------------------+----------+----------------+---------+---------------+-----------+

如何在JPA中映射为DTO对象

DTO对象字段定义如下：

  1. private Long posUserDeviceId;
  2. private Long deviceId;
  3. private String deviceImei;
  4. private String deviceMac;
  5. private String deviceUniqueCode;
  6. private String deviceType;
  7. private String deviceSystemVersion;
  8. private Long userId;
  9. private String username;
  10. private PosUserEntityConstants.UserType userType;

对象中的PosUserEntityConstants.UserType是一个自定义转换类型，通过继承AttributeConverter将Integer转换为UserType的枚举。

方法一：使用HQL的方法

Repository的查询代码如下：

  1. @Query(
  2.         value = "SELECT\n" +
  3.                 "new com.hengbao.ethiopiatelecomrecharge.dao.dto.PosUserDeviceRelationDto(\n" +
  4.                 "pdr.id,\n" +
  5.                 "pdr.deviceId,\n" +
  6.                 "pd.imei,\n" +
  7.                 "pd.mac,\n" +
  8.                 "pd.uniqueCode,\n" +
  9.                 "pd.type,\n" +
  10.                 "pd.systemVersion,\n" +
  11.                 "pdr.userId,\n" +
  12.                 "pu.userName,\n" +
  13.                 "pu.userType\n" +
  14.                 ") \n" +
  15.                 "FROM \n" +
  16.                 "PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
  17.                 "WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)",
  18.         countQuery = "SELECT count(*) FROM \n" +
  19.                 "PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
  20.                 "WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)"
  21. )
  22. Page<PosUserDeviceRelationDto> findUserAndDeviceInfoByDistributorId(Long distributorId, Pageable pageable);

可以看到HQL的方法将PosUserDeviceRelationDto的构造器直接传入到HQL语句中，省去了我们自行转换的麻烦。那么PosUserDeviceRelationDto中也要重写一个相应的构造器：

由于项目中使用了lombok，所有最终dto的代码只是在类上面加上了一些注解，@AllArgsConstructor的注解会自动生成一个全参数的构造器，构造器的顺序和字段定义顺序一致，类代码如下：

  1. @Getter
  2. @Setter
  3. @NoArgsConstructor
  4. @AllArgsConstructor
  5. @ToString
  6. public class PosUserDeviceRelationDto implements Serializable {
  7.     /**
  8.      * 版本号
  9.      */
  10.     private static final long serialVersionUID = 1L;
  12.     private Long posUserDeviceId;
  14.     private Long deviceId;
  15.     private String deviceImei;
  16.     private String deviceMac;
  17.     private String deviceUniqueCode;
  18.     private String deviceType;
  19.     private String deviceSystemVersion;
  21.     private Long userId;
  22.     private String username;
  23.     private PosUserEntityConstants.UserType userType;
  24. }

方法二：使用native query的方式查询并转换为dto

Repository的查询代码如下：

  1. @Query(
  2.         value = "SELECT\n" +
  3.                 "pdr.id,\n" +
  4.                 "pdr.device_id,\n" +
  5.                 "pd.imei,\n" +
  6.                 "pd.mac,\n" +
  7.                 "pd.unique_code,\n" +
  8.                 "pd.type,\n" +
  9.                 "pd.system_version,\n" +
  10.                 "pdr.user_id,\n" +
  11.                 "pu.user_name,\n" +
  12.                 "pu.user_type\n" +
  13.                 "FROM\n" +
  14.                 "pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
  15.                 "WHERE pdr.device_id = pd.id AND pdr.user_id = pu.id AND pdr.user_id in (select id from pos_user where distributor_id=?1)",
  16.         countQuery = "SELECT count(*) FROM\n" +
  17.                 "pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
  18.                 "WHERE pdr.device_id = pd.id AND pdr.user_id = pu.id AND pdr.user_id in (select id from pos_user where distributor_id=?1)",
  19.         nativeQuery = true
  20. )
  21. Page<Object[]> findUserAndDeviceInfoByDistributorId2(Long distributorId, Pageable pageable);

可以看到这样只能用Object[]来接收结果集，而不能直接将返回参数定义为PosUserDeviceRelationDto对象，否则会报no converter的异常。

那如何将Object[]的结果集转换为PosUserDeviceRelationDto对象呢？

首先先看一下Object[]每个对象的类型：BigInteger BigInteger String String String String String BigInteger String Integer

这是可以发现虽然mysql数据库定义的是bigint(20)类型，但是结果集是BigInteger，不能直接用Long接收，所以专门定义一个dto的构造器如下：

  1. public PosUserDeviceRelationDto(BigInteger posUserDeviceId,
  2.                                 BigInteger deviceId,
  3.                                 String deviceImei,
  4.                                 String deviceMac,
  5.                                 String deviceUniqueCode,
  6.                                 String deviceType,
  7.                                 String deviceSystemVersion,
  8.                                 BigInteger userId,
  9.                                 String username,
  10.                                 Integer userType) {
  11.     this.posUserDeviceId = posUserDeviceId == null ? null : posUserDeviceId.longValue();
  12.     this.deviceId = deviceId == null ? null : deviceId.longValue();
  13.     this.deviceImei = deviceImei;
  14.     this.deviceMac = deviceMac;
  15.     this.deviceUniqueCode = deviceUniqueCode;
  16.     this.deviceType = deviceType;
  17.     this.deviceSystemVersion = deviceSystemVersion;
  18.     this.userId = userId == null ? null : userId.longValue();
  19.     this.username = username;
  20.     // UserTypeConverter是继承自javax.persistence.AttributeConverter的类型转换器
  21.     this.userType = new PosUserEntityConstants.UserTypeConverter().convertToEntityAttribute(userType);
  22. }

然后直接调用构造即可：

  1. Page<Object[]> userAndDeviceInfoByDistributorId2 = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId2(1L, PageRequest.of(0, 10));
  2. for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
  3.     // 转换成dto的方法一：将objects中的所有参数强转为对应类型，传递到dto的构造器中；dto对象定义好对应的构造器
  4.     PosUserDeviceRelationDto dto1 = new PosUserDeviceRelationDto(
  5.             (BigInteger) objects[0],
  6.             (BigInteger) objects[1],
  7.             (String    ) objects[2],
  8.             (String    ) objects[3],
  9.             (String    ) objects[4],
  10.             (String    ) objects[5],
  11.             (String    ) objects[6],
  12.             (BigInteger) objects[7],
  13.             (String    ) objects[8],
  14.             (Integer   ) objects[9]);
  15.     System.out.println(dto1);

网上还能搜到另外一种解决方法，就是通过反射的方法简化dto的转化步骤(https://blog.csdn.net/qq_36144258/article/details/80296512)，但是csdn上这个存在bug，如果返回的objects数组中有一个值为null，那么getClass()方法获取类的类型就会报错，所以改为将每个参数的类型直接传入进去，可以这样使用反射其实省不了多少工夫了：

  1. Page<Object[]> userAndDeviceInfoByDistributorId2 = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId2(1L, PageRequest.of(0, 10));
  2. for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
  3.     // 转换成dto的方法二：反射的方法直接调用构造
  4.     PosUserDeviceRelationDto dto2 = caseDto(objects, new Class[]{BigInteger.class,
  5.                     BigInteger.class,
  6.                     String.class,
  7.                     String.class,
  8.                     String.class,
  9.                     String.class,
  10.                     String.class,
  11.                     BigInteger.class,
  12.                     String.class,
  13.                     Integer.class},
  14.             PosUserDeviceRelationDto.class);
  15.     System.out.println(dto2);
  16. }
  1. /**
  2.  * https://blog.csdn.net/qq_36144258/article/details/80296512
  3.  * 网页中直接使用objectArray中获取每一个class，但是这样有一个问题，就是如果获取的objectArray中有一个空值的话，不能获取到class，
  4.  * 导致不能获取到对象的构造器
  5.  * @param objectArray
  6.  * @param objectClassArray
  7.  * @param dtoClass
  8.  * @param <T>
  9.  * @return
  10.  */
  11. private <T> T caseDto(Object[] objectArray, Class[] objectClassArray, Class<T> dtoClass) throws Exception {
  12.     Constructor<T> constructor = dtoClass.getConstructor(objectClassArray);
  13.     return constructor.newInstance(objectArray);
  14. }

例子涉及的部分源代码

Repository

  1. @Query(
  2.         value = "SELECT\n" +
  3.                 "new com.hengbao.ethiopiatelecomrecharge.dao.dto.PosUserDeviceRelationDto(\n" +
  4.                 "pdr.id,\n" +
  5.                 "pdr.deviceId,\n" +
  6.                 "pd.imei,\n" +
  7.                 "pd.mac,\n" +
  8.                 "pd.uniqueCode,\n" +
  9.                 "pd.type,\n" +
  10.                 "pd.systemVersion,\n" +
  11.                 "pdr.userId,\n" +
  12.                 "pu.userName,\n" +
  13.                 "pu.userType\n" +
  14.                 ") \n" +
  15.                 "FROM \n" +
  16.                 "PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
  17.                 "WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)",
  18.         countQuery = "SELECT count(*) FROM \n" +
  19.                 "PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
  20.                 "WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)"
  21. )
  22. Page<PosUserDeviceRelationDto> findUserAndDeviceInfoByDistributorId(Long distributorId, Pageable pageable);
  23. @Query(
  24.         value = "SELECT\n" +
  25.                 "pdr.id,\n" +
  26.                 "pdr.device_id,\n" +
  27.                 "pd.imei,\n" +
  28.                 "pd.mac,\n" +
  29.                 "pd.unique_code,\n" +
  30.                 "pd.type,\n" +
  31.                 "pd.system_version,\n" +
  32.                 "pdr.user_id,\n" +
  33.                 "pu.user_name,\n" +
  34.                 "pu.user_type\n" +
  35.                 "FROM\n" +
  36.                 "pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
  37.                 "WHERE pdr.device_id = pd.id AND pdr.user_id = pu.id AND pdr.user_id in (select id from pos_user where distributor_id=?1)",
  38.         countQuery = "SELECT count(*) FROM\n" +
  39.                 "pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
  40.                 "WHERE pdr.device_id = pd.id AND pdr.user_id = pu.id AND pdr.user_id in (select id from pos_user where distributor_id=?1)",
  41.         nativeQuery = true
  42. )
  43. Page<Object[]> findUserAndDeviceInfoByDistributorId2(Long distributorId, Pageable pageable);

DTO类

  1. @Getter
  2. @Setter
  3. @NoArgsConstructor
  4. @AllArgsConstructor
  5. @ToString
  6. public class PosUserDeviceRelationDto implements Serializable {
  7.     /**
  8.      * 版本号
  9.      */
  10.     private static final long serialVersionUID = 1L;
  12.     private Long posUserDeviceId;
  14.     private Long deviceId;
  15.     private String deviceImei;
  16.     private String deviceMac;
  17.     private String deviceUniqueCode;
  18.     private String deviceType;
  19.     private String deviceSystemVersion;
  21.     private Long userId;
  22.     private String username;
  23.     private PosUserEntityConstants.UserType userType;
  25.     public PosUserDeviceRelationDto(BigInteger posUserDeviceId,
  26.                                     BigInteger deviceId,
  27.                                     String deviceImei,
  28.                                     String deviceMac,
  29.                                     String deviceUniqueCode,
  30.                                     String deviceType,
  31.                                     String deviceSystemVersion,
  32.                                     BigInteger userId,
  33.                                     String username,
  34.                                     Integer userType) {
  35.         this.posUserDeviceId = posUserDeviceId == null ? null : posUserDeviceId.longValue();
  36.         this.deviceId = deviceId == null ? null : deviceId.longValue();
  37.         this.deviceImei = deviceImei;
  38.         this.deviceMac = deviceMac;
  39.         this.deviceUniqueCode = deviceUniqueCode;
  40.         this.deviceType = deviceType;
  41.         this.deviceSystemVersion = deviceSystemVersion;
  42.         this.userId = userId == null ? null : userId.longValue();
  43.         this.username = username;
  44.         // UserTypeConverter是继承自javax.persistence.AttributeConverter的类型转换器
  45.         this.userType = new PosUserEntityConstants.UserTypeConverter().convertToEntityAttribute(userType);
  46.     }
  47. }

test测试类：

  1. @Test
  2. public void testFindUserAndDeviceInfoByDistributorId() throws Exception {
  3.     System.out.println("-----------------hql query-----------------");
  4.     Page<PosUserDeviceRelationDto> userAndDeviceInfoByDistributorId = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId(1L, PageRequest.of(0, 10));
  6.     System.out.println("count=" + userAndDeviceInfoByDistributorId.getTotalElements());
  7.     if(userAndDeviceInfoByDistributorId.getContent() != null) {
  8.         for (PosUserDeviceRelationDto dto : userAndDeviceInfoByDistributorId.getContent()) {
  9.             System.out.println(dto);
  10.         }
  11.     }
  13.     System.out.println("-----------------native sql query-----------------");
  14.     Page<Object[]> userAndDeviceInfoByDistributorId2 = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId2(1L, PageRequest.of(0, 10));
  15.     System.out.println("count=" + userAndDeviceInfoByDistributorId2.getTotalElements());
  16.     if(userAndDeviceInfoByDistributorId2.getContent() != null) {
  17.         for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
  18.             for (Object obj : objects) {
  19.                 System.out.print(obj + "(" + (obj == null ? null : obj.getClass().getSimpleName()) + ") ");
  20.             }
  21.             System.out.println();
  23.         }
  25.         // 转换为dto 方法一
  26.         System.out.println("-----转换dto的第一种方法-----");
  27.         for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
  28.             // 转换成dto的方法一：将objects中的所有参数强转为对应类型，传递到dto的构造器中；dto对象定义好对应的构造器
  29.             PosUserDeviceRelationDto dto1 = new PosUserDeviceRelationDto(
  30.                     (BigInteger) objects[0],
  31.                     (BigInteger) objects[1],
  32.                     (String    ) objects[2],
  33.                     (String    ) objects[3],
  34.                     (String    ) objects[4],
  35.                     (String    ) objects[5],
  36.                     (String    ) objects[6],
  37.                     (BigInteger) objects[7],
  38.                     (String    ) objects[8],
  39.                     (Integer   ) objects[9]);
  40.             System.out.println(dto1);
  41.         }
  43.         // 转换为dto 方法二
  44.         System.out.println("-----转换dto的第二种方法-----");
  45.         for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
  46.             // 转换成dto的方法二：反射的方法直接调用构造
  47.             PosUserDeviceRelationDto dto2 = caseDto(objects, new Class[]{BigInteger.class,
  48.                             BigInteger.class,
  49.                             String.class,
  50.                             String.class,
  51.                             String.class,
  52.                             String.class,
  53.                             String.class,
  54.                             BigInteger.class,
  55.                             String.class,
  56.                             Integer.class},
  57.                     PosUserDeviceRelationDto.class);
  58.             System.out.println(dto2);
  59.         }
  60.     }
  61. }
  63. /**
  64.  * https://blog.csdn.net/qq_36144258/article/details/80296512
  65.  * 网页中直接使用objectArray中获取每一个class，但是这样有一个问题，就是如果获取的objectArray中有一个空值的话，不能获取到class，
  66.  * 导致不能获取到对象的构造器
  67.  * @param objectArray
  68.  * @param objectClassArray
  69.  * @param dtoClass
  70.  * @param <T>
  71.  * @return
  72.  */
  73. private <T> T caseDto(Object[] objectArray, Class[] objectClassArray, Class<T> dtoClass) throws Exception {
  74.     Constructor<T> constructor = dtoClass.getConstructor(objectClassArray);
  75.     return constructor.newInstance(objectArray);
  76. }

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