jpa2.2.10 Query 使用entityManager构建sql查询返回Dto，实体类和Dto中都有set<实体类>集合，不使用xml配置，不使用for进行转换，写个详细的示例

好的，针对您的问题，我可以提供以下示例代码：

实体类 User.java：

@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @OneToMany(mappedBy = "user", cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<Address> addresses;

    // getters and setters
}

实体类 Address.java：

@Entity
@Table(name = "address")
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "street")
    private String street;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;

    // getters and setters
}

Dto 类 UserDto.java：

public class UserDto {
    private Long id;
    private String name;
    private Set<AddressDto> addresses;

    // getters and setters
}

Dto 类 AddressDto.java：

public class AddressDto {
    private Long id;
    private String street;

    // getters and setters
}

然后，在查询中可以使用 entityManager 创建 NativeQuery，并使用 JPA 的构造函数表达式进行转换，代码示例如下：

String sql = "SELECT u.id AS id, u.name AS name, a.id AS address_id, a.street AS street " +
        "FROM user u " +
        "LEFT JOIN address a ON u.id = a.user_id " +
        "WHERE u.id = :userId";

List<UserDto> userDtos = entityManager.createNativeQuery(sql, "userDtoMapping")
        .setParameter("userId", userId)
        .getResultList();

其中，“userDtoMapping” 是在 EntityManagerFactory 中配置的实体映射关系，示例代码如下：

Map<String, Class<?>> entityClassMap = new HashMap<>();
entityClassMap.put("userDtoMapping", UserDto.class);
entityClassMap.put("addressDtoMapping", AddressDto.class);

HibernateJpaVendorAdapter jpaVendorAdapter = new HibernateJpaVendorAdapter();
jpaVendorAdapter.setGenerateDdl(false);

LocalContainerEntityManagerFactoryBean factoryBean = new LocalContainerEntityManagerFactoryBean();
factoryBean.setJpaVendorAdapter(jpaVendorAdapter);
factoryBean.setPackagesToScan("com.example.domain");
factoryBean.setMappingResources("META-INF/orm.xml");
factoryBean.setMappingClasses(User.class, Address.class);
factoryBean.setJpaPropertyMap(properties);
factoryBean.setEntityNameResolvers(Collections.singletonList(new AnnotationMetadataEntityNameResolver()));
factoryBean.setPersistenceUnitName("unitName");
factoryBean.setEntityMappings(createEntityMappings(entityClassMap));

private static InputStream createEntityMappings(Map<String, Class<?>> entityClassMap) {
    StringWriter writer = new StringWriter();
    XStream xStream = new XStream(new DomXmlWriterFactory());
    xStream.autodetectAnnotations(true);
    xStream.alias("entity-mappings", Object.class);
    xStream.alias("entity", Object.class);
    xStream.alias("field", Object.class);
    xStream.useAttributeFor(Field.class, "name");
    xStream.aliasField("name", Field.class, "name");
    xStream.aliasField("column-name", Field.class, "columnName");
    xStream.aliasField("entity-class", Object.class, "entityClass");
    xStream.aliasField("class", Object.class, "entityClass");
    xStream.aliasField("entity-name", Object.class, "entityName");
    xStream.aliasField("table", Object.class, "tableName");
    xStream.aliasField("id-class", Object.class, "idClass");
    xStream.aliasField("id", Object.class, "idFieldName");
    xStream.aliasField("sequence-generator", Object.class, "sequenceGenerator");
    xStream.aliasField("table-generator", Object.class, "tableGenerator");
    xStream.aliasField("query", Object.class, "query");

    entityClassMap.forEach((mapping, clazz) -> {
        xStream.addImplicitMap(Field.class, "fields", "field", Field.class);
        xStream.useAttributeFor(AddressDto.class, "id");
        xStream.useAttributeFor(AddressDto.class, "street");

        xStream.alias(mapping, EntityMappings.class);
        xStream.alias(mapping + "-entity", Entity.class);
        xStream.alias(mapping + "-field", Field.class);

        EntityMappings entityMappings = new EntityMappings();
        Entity entity = new Entity();
        entity.setEntityClass(clazz.getName());

        Reflections fieldReflections = new Reflections(clazz);
        Set<Field> fields = fieldReflections.getFieldsAnnotatedWith(Column.class).stream()
                .map(field -> {
                    Column column = field.getAnnotation(Column.class);
                    Field f = new Field();
                    f.setName(field.getName());
                    f.setColumnName(column.name());
                    return f;
                })
                .collect(Collectors.toSet());
        entity.setFields(fields);

        entityMappings.addEntity(entity);
        try {
            xStream.toXML(entityMappings, writer);
        } catch (Exception e) {
           // handle exception
        }
    });
    return new ByteArrayInputStream(writer.toString().getBytes());
}

这样，使用 JPA 构建 SQL 查询，并将结果转换为 Dto 对象集合，便不需要手动遍历集合进行类型转换了。