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
CREATE TABLE `pos_user` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`user_name` varchar(50) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`user_pwd` varchar(255) DEFAULT NULL,
`user_type` int(11) DEFAULT NULL,
`parent_id` bigint(20) DEFAULT NULL,
`user_status` int(11) DEFAULT NULL,
`distributor_id` bigint(20) DEFAULT NULL,
`creator_identity_type` int(2) DEFAULT NULL,
`creator_id` bigint(20) DEFAULT NULL,
`create_date` varchar(50) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=22 DEFAULT CHARSET=utf8;
设备表
CREATE TABLE `pos_device` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`imei` varchar(120) NOT NULL,
`mac` varchar(120) NOT NULL,
`unique_code` varchar(120) CHARACTER SET utf8 COLLATE utf8_bin DEFAULT NULL,
`type` varchar(100) DEFAULT NULL,
`system_version` varchar(100) DEFAULT NULL,
`distributor_id` bigint(20) DEFAULT NULL,
`creator_identity_type` int(2) DEFAULT NULL,
`creator_id` bigint(20) DEFAULT NULL,
`create_date` varchar(50) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=31 DEFAULT CHARSET=utf8;
用户和设备关联表
CREATE TABLE `pos_user_device_relation` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`device_id` bigint(20) DEFAULT NULL,
`user_id` bigint(20) DEFAULT NULL,
PRIMARY KEY (`id`)
) 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
SELECT
pdr.id,
pdr.device_id,
pd.imei,
pd.mac,
pd.unique_code,
pd.type,
pd.system_version,
pdr.user_id,
pu.user_name,
pu.user_type
FROM
pos_user_device_relation pdr, pos_user pu, pos_device pd
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：
+----+-----------+---------------------+-------------------+--------------------------+----------+----------------+---------+---------------+-----------+
| id | device_id | imei | mac | unique_code | type | system_version | user_id | user_name | user_type |
+----+-----------+---------------------+-------------------+--------------------------+----------+----------------+---------+---------------+-----------+
如何在JPA中映射为DTO对象
DTO对象字段定义如下：
private Long posUserDeviceId;
private Long deviceId;
private String deviceImei;
private String deviceMac;
private String deviceUniqueCode;
private String deviceType;
private String deviceSystemVersion;
private Long userId;
private String username;
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：
@Query(
value = "SELECT\n" +
"new com.hengbao.ethiopiatelecomrecharge.dao.dto.PosUserDeviceRelationDto(\n" +
"pdr.id,\n" +
"pdr.deviceId,\n" +
"pd.imei,\n" +
"pd.mac,\n" +
"pd.uniqueCode,\n" +
"pd.type,\n" +
"pd.systemVersion,\n" +
"pdr.userId,\n" +
"pu.userName,\n" +
"pu.userType\n" +
") \n" +
"FROM \n" +
"PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
"WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)",
countQuery = "SELECT count(*) FROM \n" +
"PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
"WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)"
)
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：
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class PosUserDeviceRelationDto implements Serializable {
/**
* 版本号
*/
private static final long serialVersionUID = 1L;
private Long posUserDeviceId;
private Long deviceId;
private String deviceImei;
private String deviceMac;
private String deviceUniqueCode;
private String deviceType;
private String deviceSystemVersion;
private Long userId;
private String username;
private PosUserEntityConstants.UserType userType;
}
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：
@Query(
value = "SELECT\n" +
"pdr.id,\n" +
"pdr.device_id,\n" +
"pd.imei,\n" +
"pd.mac,\n" +
"pd.unique_code,\n" +
"pd.type,\n" +
"pd.system_version,\n" +
"pdr.user_id,\n" +
"pu.user_name,\n" +
"pu.user_type\n" +
"FROM\n" +
"pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
"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)",
countQuery = "SELECT count(*) FROM\n" +
"pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
"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)",
nativeQuery = true
)
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：
public PosUserDeviceRelationDto(BigInteger posUserDeviceId,
BigInteger deviceId,
String deviceImei,
String deviceMac,
String deviceUniqueCode,
String deviceType,
String deviceSystemVersion,
BigInteger userId,
String username,
Integer userType) {
this.posUserDeviceId = posUserDeviceId == null ? null : posUserDeviceId.longValue();
this.deviceId = deviceId == null ? null : deviceId.longValue();
this.deviceImei = deviceImei;
this.deviceMac = deviceMac;
this.deviceUniqueCode = deviceUniqueCode;
this.deviceType = deviceType;
this.deviceSystemVersion = deviceSystemVersion;
this.userId = userId == null ? null : userId.longValue();
this.username = username;
// UserTypeConverter是继承自javax.persistence.AttributeConverter的类型转换器
this.userType = new PosUserEntityConstants.UserTypeConverter().convertToEntityAttribute(userType);
}
然后直接调用构造即可：
Page<Object[]> userAndDeviceInfoByDistributorId2 = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId2(1L, PageRequest.of(0, 10));
for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
// 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
PosUserDeviceRelationDto dto1 = new PosUserDeviceRelationDto(
(BigInteger) objects[0],
(BigInteger) objects[1],
(String ) objects[2],
(String ) objects[3],
(String ) objects[4],
(String ) objects[5],
(String ) objects[6],
(BigInteger) objects[7],
(String ) objects[8],
(Integer ) objects[9]);
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：
Page<Object[]> userAndDeviceInfoByDistributorId2 = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId2(1L, PageRequest.of(0, 10));
for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
// 转换成dto的方法二：反射的方法直接调用构造
PosUserDeviceRelationDto dto2 = caseDto(objects, new Class[]{BigInteger.class,
BigInteger.class,
String.class,
String.class,
String.class,
String.class,
String.class,
BigInteger.class,
String.class,
Integer.class},
PosUserDeviceRelationDto.class);
System.out.println(dto2);
}
/**
* https://blog.csdn.net/qq_36144258/article/details/80296512
* 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，
* 导致不能获取到对象的构造器
* @param objectArray
* @param objectClassArray
* @param dtoClass
* @param <T>
* @return
*/
private <T> T caseDto(Object[] objectArray, Class[] objectClassArray, Class<T> dtoClass) throws Exception {
Constructor<T> constructor = dtoClass.getConstructor(objectClassArray);
return constructor.newInstance(objectArray);
}
例子涉及的部分源代码
Repository
@Query(
value = "SELECT\n" +
"new com.hengbao.ethiopiatelecomrecharge.dao.dto.PosUserDeviceRelationDto(\n" +
"pdr.id,\n" +
"pdr.deviceId,\n" +
"pd.imei,\n" +
"pd.mac,\n" +
"pd.uniqueCode,\n" +
"pd.type,\n" +
"pd.systemVersion,\n" +
"pdr.userId,\n" +
"pu.userName,\n" +
"pu.userType\n" +
") \n" +
"FROM \n" +
"PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
"WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)",
countQuery = "SELECT count(*) FROM \n" +
"PosUserDeviceRelationEntity pdr, PosUserEntity pu, PosDeviceEntity pd \n" +
"WHERE pdr.deviceId = pd.id AND pdr.userId = pu.id AND pdr.userId in (select id from PosUserEntity where distributorId=?1)"
)
Page<PosUserDeviceRelationDto> findUserAndDeviceInfoByDistributorId(Long distributorId, Pageable pageable);
@Query(
value = "SELECT\n" +
"pdr.id,\n" +
"pdr.device_id,\n" +
"pd.imei,\n" +
"pd.mac,\n" +
"pd.unique_code,\n" +
"pd.type,\n" +
"pd.system_version,\n" +
"pdr.user_id,\n" +
"pu.user_name,\n" +
"pu.user_type\n" +
"FROM\n" +
"pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
"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)",
countQuery = "SELECT count(*) FROM\n" +
"pos_user_device_relation pdr, pos_user pu, pos_device pd\n" +
"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)",
nativeQuery = true
)
Page<Object[]> findUserAndDeviceInfoByDistributorId2(Long distributorId, Pageable pageable);
DTO类
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class PosUserDeviceRelationDto implements Serializable {
/**
* 版本号
*/
private static final long serialVersionUID = 1L;
private Long posUserDeviceId;
private Long deviceId;
private String deviceImei;
private String deviceMac;
private String deviceUniqueCode;
private String deviceType;
private String deviceSystemVersion;
private Long userId;
private String username;
private PosUserEntityConstants.UserType userType;
public PosUserDeviceRelationDto(BigInteger posUserDeviceId,
BigInteger deviceId,
String deviceImei,
String deviceMac,
String deviceUniqueCode,
String deviceType,
String deviceSystemVersion,
BigInteger userId,
String username,
Integer userType) {
this.posUserDeviceId = posUserDeviceId == null ? null : posUserDeviceId.longValue();
this.deviceId = deviceId == null ? null : deviceId.longValue();
this.deviceImei = deviceImei;
this.deviceMac = deviceMac;
this.deviceUniqueCode = deviceUniqueCode;
this.deviceType = deviceType;
this.deviceSystemVersion = deviceSystemVersion;
this.userId = userId == null ? null : userId.longValue();
this.username = username;
// UserTypeConverter是继承自javax.persistence.AttributeConverter的类型转换器
this.userType = new PosUserEntityConstants.UserTypeConverter().convertToEntityAttribute(userType);
}
}
test测试类：
@Test
public void testFindUserAndDeviceInfoByDistributorId() throws Exception {
System.out.println("-----------------hql query-----------------");
Page<PosUserDeviceRelationDto> userAndDeviceInfoByDistributorId = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId(1L, PageRequest.of(0, 10));
System.out.println("count=" + userAndDeviceInfoByDistributorId.getTotalElements());
if(userAndDeviceInfoByDistributorId.getContent() != null) {
for (PosUserDeviceRelationDto dto : userAndDeviceInfoByDistributorId.getContent()) {
System.out.println(dto);
}
}
System.out.println("-----------------native sql query-----------------");
Page<Object[]> userAndDeviceInfoByDistributorId2 = posUserDeviceRelationRepository.findUserAndDeviceInfoByDistributorId2(1L, PageRequest.of(0, 10));
System.out.println("count=" + userAndDeviceInfoByDistributorId2.getTotalElements());
if(userAndDeviceInfoByDistributorId2.getContent() != null) {
for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
for (Object obj : objects) {
System.out.print(obj + "(" + (obj == null ? null : obj.getClass().getSimpleName()) + ") ");
}
System.out.println();
}
// 转换为dto 方法一
System.out.println("-----转换dto的第一种方法-----");
for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
// 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
PosUserDeviceRelationDto dto1 = new PosUserDeviceRelationDto(
(BigInteger) objects[0],
(BigInteger) objects[1],
(String ) objects[2],
(String ) objects[3],
(String ) objects[4],
(String ) objects[5],
(String ) objects[6],
(BigInteger) objects[7],
(String ) objects[8],
(Integer ) objects[9]);
System.out.println(dto1);
}
// 转换为dto 方法二
System.out.println("-----转换dto的第二种方法-----");
for (Object[] objects : userAndDeviceInfoByDistributorId2.getContent()) {
// 转换成dto的方法二：反射的方法直接调用构造
PosUserDeviceRelationDto dto2 = caseDto(objects, new Class[]{BigInteger.class,
BigInteger.class,
String.class,
String.class,
String.class,
String.class,
String.class,
BigInteger.class,
String.class,
Integer.class},
PosUserDeviceRelationDto.class);
System.out.println(dto2);
}
}
}
/**
* https://blog.csdn.net/qq_36144258/article/details/80296512
* 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，
* 导致不能获取到对象的构造器
* @param objectArray
* @param objectClassArray
* @param dtoClass
* @param <T>
* @return
*/
private <T> T caseDto(Object[] objectArray, Class[] objectClassArray, Class<T> dtoClass) throws Exception {
Constructor<T> constructor = dtoClass.getConstructor(objectClassArray);
return constructor.newInstance(objectArray);
}