在我的DAO图层中,我有一个像这样的查找功能
public List<?> findCategoryWithSentenceNumber(int offset, int maxRec) {
Criteria crit = getSession().createCriteria(Category.class, "cate");
crit.createAlias("cate.sentences", "sent");
crit.setProjection(Projections.projectionList().
add(Projections.property("title"), "title").
add(Projections.count("sent.id"), "numberOfSentence").
add(Projections.groupProperty("title"))
);
crit.setFirstResult(offset);
crit.setMaxResults(maxRec);
return crit.list();
}
所以,为了读取数据,我必须使用一个循环(Iterator
)
List<?> result = categoryDAO.findCategoryWithSentenceNumber(0, 10);
// List<DQCategoryDTO> dtoList = new ArrayList<>();
for (Iterator<?> it = result.iterator(); it.hasNext(); ) {
Object[] myResult = (Object[]) it.next();
String title = (String) myResult[0];
Long count = (Long) myResult[1];
assertEquals("test", title);
assertEquals(1, count.intValue());
// dQCategoryDTO = new DQCategoryDTO();
// dQCategoryDTO.setTitle(title);
// dQCategoryDTO.setNumberOfSentence(count);
// dtoList.add(dQCategoryDTO);
}
我的问题是:是否有任何api,框架可以轻松地将List<?> result
转换为DTO
对象列表(例如,DQCategoryDTO),而无需使用任何循环,迭代器和调用setter / getter填这个价值?
答案 0 :(得分:11)
正如我在this article中所解释的那样,您有很多选项可以将投影映射到DTO结果集:
tsconfig.json
List<Tuple> postDTOs = entityManager.createQuery(
"select " +
" p.id as id, " +
" p.title as title " +
"from Post p " +
"where p.createdOn > :fromTimestamp", Tuple.class)
.setParameter( "fromTimestamp", Timestamp.from(
LocalDateTime.of( 2016, 1, 1, 0, 0, 0 )
.toInstant( ZoneOffset.UTC ) ))
.getResultList();
assertFalse( postDTOs.isEmpty() );
Tuple postDTO = postDTOs.get( 0 );
assertEquals(
1L,
postDTO.get( "id" )
);
这个可以从Hibernate 5.2.11获得,这是升级的另一个原因。
List<PostDTO> postDTOs = entityManager.createQuery(
"select new " +
" com.vladmihalcea.book.hpjp.hibernate.query.dto.projection.jpa.PostDTO(" +
" p.id, " +
" p.title " +
" ) " +
"from Post p " +
"where p.createdOn > :fromTimestamp", PostDTO.class)
.setParameter( "fromTimestamp", Timestamp.from(
LocalDateTime.of( 2016, 1, 1, 0, 0, 0 )
.toInstant( ZoneOffset.UTC ) ))
.getResultList();
如果我们使用之前介绍的相同List<Tuple> postDTOs = entityManager.createNativeQuery(
"SELECT " +
" p.id AS id, " +
" p.title AS title " +
"FROM Post p " +
"WHERE p.created_on > :fromTimestamp", Tuple.class)
.setParameter( "fromTimestamp", Timestamp.from(
LocalDateTime.of( 2016, 1, 1, 0, 0, 0 )
.toInstant( ZoneOffset.UTC ) ))
.getResultList();
类类型,我们必须提供以下PostDTO
:
@SqlResultSetMapping
现在,名为native query的SQL投影执行如下:
@NamedNativeQuery(
name = "PostDTO",
query =
"SELECT " +
" p.id AS id, " +
" p.title AS title " +
"FROM Post p " +
"WHERE p.created_on > :fromTimestamp",
resultSetMapping = "PostDTO"
)
@SqlResultSetMapping(
name = "PostDTO",
classes = @ConstructorResult(
targetClass = PostDTO.class,
columns = {
@ColumnResult(name = "id"),
@ColumnResult(name = "title")
}
)
)
这一次,你的DTO需要让你需要Hibernate的属性的setter从底层的JDBC List<PostDTO> postDTOs = entityManager.createNamedQuery("PostDTO")
.setParameter( "fromTimestamp", Timestamp.from(
LocalDateTime.of( 2016, 1, 1, 0, 0, 0 )
.toInstant( ZoneOffset.UTC ) ))
.getResultList();
中填充。
DTO预测如下:
ResultSet
List<PostDTO> postDTOs = entityManager.createQuery(
"select " +
" p.id as id, " +
" p.title as title " +
"from Post p " +
"where p.createdOn > :fromTimestamp")
.setParameter( "fromTimestamp", Timestamp.from(
LocalDateTime.of( 2016, 1, 1, 0, 0, 0 ).toInstant( ZoneOffset.UTC ) ))
.unwrap( org.hibernate.query.Query.class )
.setResultTransformer( Transformers.aliasToBean( PostDTO.class ) )
.getResultList();
答案 1 :(得分:4)
您可以使用可以从别名转换为bean(DTO)属性的ResultTransformer。有关用法,请参阅第13.1.5节
中的Hibernate docs here答案 2 :(得分:1)
以下是使用Projection根据街道名称将地址组合在一起的完整示例。
Criteria criteria = getCurrentSession().createCriteria(Address.class);
// adding condition
criteria.add(Restrictions.eq("zip", "12345"));
// adding projection
criteria.setProjection(Projections.projectionList()
.add(Projections.groupProperty("streetName"), "streetName")
.add(Projections.count("apartment"), "count"));
// set transformer
criteria.setResultTransformer(new AliasToBeanResultTransformer(SomeDTO.class));
List<SomeDTO> someDTOs = criteria.list();
someDTOs列表将包含streetName的结果组数。每个SomeDTO对象都包含该街道的街道名称和公寓数量。
SomeDTO.java
public class SomeDTO{
private String streetName;
private Long count;
public void setStreetName(String streetName){
this.streetName=streetName;
}
public String getStreetName(){
return this.streetName;
}
public Long getCount() {
return count;
}
public void setCount(Long count) {
this.count = count;
}
}
答案 3 :(得分:0)
这正是为其创建Blaze-Persistence Entity Views的用例!
您的DTO看起来像
@EntityView(Category.class)
interface DQCategoryDTO {
String getTitle();
@Mapping("SIZE(sentences)")
int getCount();
}
,如果您使用Spring Data,则可以在类似的存储库中使用它
interface CategoryRepository extends Repository<Category, Long> {
List<DQCategoryDTO> findAll(Pageable pageable);
}