Spring Data Jpa 原生SQL返回自定义对象最简洁方式

Jonathan · 2020 年11 月 30 日 14:22

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<UserName> findByName(String name);
  // 方式2
  2. @Query(value = "select name from t_users where name = ?", nativeQuery = true)
   List<UserName> 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<ConvertiblePair> 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> T map2Pojo(Object entity, Class<T> 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

@Configuration
public class JpaConfig {

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

测试

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

@Data
@ToString
@NoArgsConstructor
public 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<UserName> a = usersRepository.findByName("A");
      System.out.println(a);
   }

   /**
    * 自定义sql 自定义对象
    */
   @Test
   void t3() {
      List<UserName> 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

@Nullable
protected 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);

@Nullable
public GenericConverter find(TypeDescriptor sourceType, TypeDescriptor targetType) {
   // Search the full type hierarchy
   // 获取 
   List<Class<?>> sourceCandidates = getClassHierarchy(sourceType.getType());
   List<Class<?>> 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)

@Nullable
private 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<ConvertiblePair, ConvertersForPair> 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

原文：Spring Data Jpa 原生SQL返回自定义对象最简洁方式 - evan888的个人空间 - OSCHINA - 中文开源技术交流社区
作者：evan888