Spring Data Jpa原生SQL返回自定义对象最简洁方式是什么

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Spring Data Jpa 原生SQL返回自定义对象最简洁方式

此文章只讨论两种方式查询, 使用jpa关键字查询和自定义sql

  // 方式1      1. List findByName(String name);  // 方式2  2. @Query(value = "select name from t_users where name = ?", nativeQuery = true)   List findByName2(String name);

使用接口接收

即通过定义一个接口接口 UserName，两种方式都支持通过定义接口接受返回，JPA原生支持

public interface UserName {   String getNname();}

自定义对象接收

方式一 JAP原生支持自定义对象，但条件是而且只有一个构造函数，有些工具类需要用到默认构造函数，不方便

方式二 JAP不支持自定义对象，会返回Object[] 对象数组

解决方案

例子只是解决方式二， 如果需要解决方式一构造函数问题，可以借鉴，下面例子自己实现 我们定义一个接口ReabamDTO

public interface ReabamDTO {}

GenericConverter实现类

内容是map 转 ReabamDTO

public final class JpaConvert implements GenericConverter {   @Override   public Set getConvertibleTypes() {      return Collections.singleton(new ConvertiblePair(Map.class, ReabamDTO.class));   }   @Override   public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {      return map2Pojo(source, targetType.getObjectType());   }   public static  T map2Pojo(Object entity, Class tClass) {      CopyOptions copyOptions = CopyOptions.create()            .setIgnoreCase(true)            .setIgnoreError(true)            .setIgnoreNullValue(true)            .setFieldNameEditor(StrUtil::toUnderlineCase);      return BeanUtil.toBean(entity, tClass, copyOptions);   }}

将自定义convert加入到GenericConversionService

@Configurationpublic class JpaConfig {   @PostConstruct   public void init() {      GenericConversionService genericConversionService = ((GenericConversionService) DefaultConversionService.getSharedInstance());      genericConversionService.addConverter(new JpaConvert());   }}

测试

public interface UsersRepository extends JpaRepository {       List findByName(String name);       @Query(value = "select name from t_users where name = ?", nativeQuery = true)   List findByName2(String name);}

@Data@ToString@NoArgsConstructorpublic class UserName implements ReabamDTO {   private String name;}

@RunWith(SpringJUnit4ClassRunner.class)@SpringBootTest(classes = DemoApplication.class, properties = {"spring.profiles.active=local"})class DemoApplicationTests {   @Autowired   private UsersRepository usersRepository;   @Test   void contextLoads() {      Users users = new Users();      users.setName("A");      users.setAge(1);      users.setAddress("AA");      usersRepository.save(users);   }   /**    * 非自定义sql可以返回自定义对象    */   @Test   void t2() {      List a = usersRepository.findByName("A");      System.out.println(a);   }   /**    * 自定义sql 自定义对象    */   @Test   void t3() {      List a = usersRepository.findByName2("A");      System.out.println(a);   }}

原理可选择观看

查看报错信息，找不到转换器异常， 那么只需要加入对应的装换器就可以了，

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [com.architeture.demo.UserName]at org.springframework.core.convert.support.GenericConversionService.handleConverterNotFound(GenericConversionService.java:322)at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:195)at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:175)at org.springframework.data.repository.query.ResultProcessor$ProjectingConverter.convert(ResultProcessor.java:309)at org.springframework.data.repository.query.ResultProcessor$ChainingConverter.lambda$and$0(ResultProcessor.java:225)at org.springframework.data.repository.query.ResultProcessor$ChainingConverter.convert(ResultProcessor.java:236)at org.springframework.data.repository.query.ResultProcessor.processResult(ResultProcessor.java:156)at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:158)at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:143)

通过查看源码， 获取转换器的位置 org.springframework.core.convert.support.GenericConversionService#getConverter

@Nullableprotected GenericConverter getConverter(TypeDescriptor sourceType, TypeDescriptor targetType) {   ConverterCacheKey key = new ConverterCacheKey(sourceType, targetType);   GenericConverter converter = this.converterCache.get(key);   if (converter != null) {      return (converter != NO_MATCH ? converter : null);   }   converter = this.converters.find(sourceType, targetType);   if (converter == null) {      converter = getDefaultConverter(sourceType, targetType);   }   if (converter != null) {      this.converterCache.put(key, converter);      return converter;   }   this.converterCache.put(key, NO_MATCH);   return null;}

继续看源码， 查找能加入转换器位置 converter = this.converters.find(sourceType, targetType);

@Nullablepublic GenericConverter find(TypeDescriptor sourceType, TypeDescriptor targetType) {   // Search the full type hierarchy   // 获取    List> sourceCandidates = getClassHierarchy(sourceType.getType());   List> targetCandidates = getClassHierarchy(targetType.getType());   for (Class sourceCandidate : sourceCandidates) {      for (Class targetCandidate : targetCandidates) {         ConvertiblePair convertiblePair = new ConvertiblePair(sourceCandidate, targetCandidate);         GenericConverter converter = getRegisteredConverter(sourceType, targetType, convertiblePair);         if (converter != null) {            return converter;         }      }   }   return null;}

此方法 源对象TupBackedMap父类或接口和UserName父类或接口进行组合，获取到对应的转换器

TupBackedMap的父类或接口

org.springframework.core.convert.support.GenericConversionService#addConverter(org.springframework.core.convert.converter.GenericConverter)

@Nullableprivate GenericConverter getRegisteredConverter(TypeDescriptor sourceType,      TypeDescriptor targetType, ConvertiblePair convertiblePair) {   // Check specifically registered converters   ConvertersForPair convertersForPair = this.converters.get(convertiblePair);   if (convertersForPair != null) {      GenericConverter converter = convertersForPair.getConverter(sourceType, targetType);      if (converter != null) {         return converter;      }   }   // Check ConditionalConverters for a dynamic match   for (GenericConverter globalConverter : this.globalConverters) {      if (((ConditionalConverter) globalConverter).matches(sourceType, targetType)) {         return globalConverter;      }   }   return null;}

可以看到在 ConvertersForPair convertersForPair = this.converters.get(convertiblePair); 在convertes中加入转换器

org.springframework.core.convert.support.GenericConversionService.Converters

private static class Converters {   private final Map converters = new LinkedHashMap<>(36);   public void add(GenericConverter converter) {   }}

查看调用 add 方法位置， org.springframework.core.convert.support.GenericConversionService#addConverter(org.springframework.core.convert.converter.GenericConverter) 最终定位到这里

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