Question

我在我的代码中使用Criteria Query。它始终触发select * from ...

相反，我想从我的查询中忽略一个列（字段），因为该字段有大量以字节存储的数据。这导致了性能问题。

任何人都可以为此提出想法吗？

部分更新

我在查询中添加了一个投影，它创建了一个类似...的查询

select
    this_.TEMPLATE_ID as y0_,
    this_.TEMPLATE_NAME as y1_,
    this_.CREATE_DATE as y2_,
    this_.UPDATE_DATE as y3_,
    this_.STATUS_CODE as y4_,
    this_.USER_ID as y5_,
    this_.UPDATED_BY as y6_,
    this_.CATEGORY_ID as y7_,
    this_.PRACTICE_ID as y8_ 
from
    templates this_ 
inner join
    user user1_ 
        on this_.USER_ID=user1_.USER_ID 
inner join
    template_categories category2_ 
        on this_.CATEGORY_ID=category2_.CATEGORY_ID 
where
    y4_=? 
    and y8_=? 
    and y5_ in (
        ?, ?
    ) 
order by
    y1_ asc limit ?

现在问题就像... Unknown column 'y4_' in 'where clause' 和y8_相同的错误，y5_表示所有关闭的地方都给出了错误。

我将其修改为像...一样查询

select
    this_.TEMPLATE_ID as y0_,
    this_.TEMPLATE_NAME as y1_,
    this_.CREATE_DATE as y2_,
    this_.UPDATE_DATE as y3_,
    this_.STATUS_CODE as y4_,
    this_.USER_ID as y5_,
    this_.UPDATED_BY as y6_,
    this_.CATEGORY_ID as y7_,
    this_.PRACTICE_ID as y8_ 
from
    templates this_ 
inner join
    user user1_ 
        on this_.USER_ID=user1_.USER_ID 
inner join
    template_categories category2_ 
        on this_.CATEGORY_ID=category2_.CATEGORY_ID 
where
    this_.STATUS_CODE=1
    and this_.PRACTICE_ID=1 
    and this_.USER_ID in (
        1, 2
    ) 
order by
    y1_ asc limit ?

它有效。但我不知道如何在HQL中修改它？

Answer 1

使用Projections指定要返回的列。

示例

SQL查询

SELECT user.id, user.name FROM user;

Hibernate Alternative

Criteria cr = session.createCriteria(User.class) .setProjection(Projections.projectionList() .add(Projections.property("id"), "id") .add(Projections.property("Name"), "Name")) .setResultTransformer(Transformers.aliasToBean(User.class)); List<User> list = cr.list();

Answer 2

您可以将JPQL以及JPA Criteria API用于任何类型的DTO投影（仅将选定的列映射到DTO类）。查看下面的代码段，这些代码段显示如何有选择地选择各种列而不是选择所有列。这些示例还显示了如何从中选择各种列连接多列。我希望这有帮助。

JPQL代码：

String dtoProjection = "new com.katariasoft.technologies.jpaHibernate.college.data.dto.InstructorDto"
                + "(i.id, i.name, i.fatherName, i.address, id.proofNo, "
                + " v.vehicleNumber, v.vechicleType, s.name, s.fatherName, "
                + " si.name, sv.vehicleNumber , svd.name) ";

        List<InstructorDto> instructors = queryExecutor.fetchListForJpqlQuery(
                "select " + dtoProjection + " from Instructor i " + " join i.idProof id " + " join i.vehicles v "
                        + " join i.students s " + " join s.instructors si " + " join s.vehicles sv "
                        + " join sv.documents svd " + " where i.id > :id and svd.name in (:names) "
                        + " order by i.id , id.proofNo , v.vehicleNumber , si.name , sv.vehicleNumber , svd.name ",
                CollectionUtils.mapOf("id", 2, "names", Arrays.asList("1", "2")), InstructorDto.class);

        if (Objects.nonNull(instructors))
            instructors.forEach(i -> i.setName("Latest Update"));

        DataPrinters.listDataPrinter.accept(instructors);

JPA Criteria API代码：

@Test
    public void fetchFullDataWithCriteria() {
        CriteriaBuilder cb = criteriaUtils.criteriaBuilder();
        CriteriaQuery<InstructorDto> cq = cb.createQuery(InstructorDto.class);

        // prepare from expressions
        Root<Instructor> root = cq.from(Instructor.class);
        Join<Instructor, IdProof> insIdProofJoin = root.join(Instructor_.idProof);
        Join<Instructor, Vehicle> insVehicleJoin = root.join(Instructor_.vehicles);
        Join<Instructor, Student> insStudentJoin = root.join(Instructor_.students);
        Join<Student, Instructor> studentInsJoin = insStudentJoin.join(Student_.instructors);
        Join<Student, Vehicle> studentVehicleJoin = insStudentJoin.join(Student_.vehicles);
        Join<Vehicle, Document> vehicleDocumentJoin = studentVehicleJoin.join(Vehicle_.documents);

        // prepare select expressions.
        CompoundSelection<InstructorDto> selection = cb.construct(InstructorDto.class, root.get(Instructor_.id),
                root.get(Instructor_.name), root.get(Instructor_.fatherName), root.get(Instructor_.address),
                insIdProofJoin.get(IdProof_.proofNo), insVehicleJoin.get(Vehicle_.vehicleNumber),
                insVehicleJoin.get(Vehicle_.vechicleType), insStudentJoin.get(Student_.name),
                insStudentJoin.get(Student_.fatherName), studentInsJoin.get(Instructor_.name),
                studentVehicleJoin.get(Vehicle_.vehicleNumber), vehicleDocumentJoin.get(Document_.name));

        // prepare where expressions.
        Predicate instructorIdGreaterThan = cb.greaterThan(root.get(Instructor_.id), 2);
        Predicate documentNameIn = cb.in(vehicleDocumentJoin.get(Document_.name)).value("1").value("2");
        Predicate where = cb.and(instructorIdGreaterThan, documentNameIn);

        // prepare orderBy expressions.
        List<Order> orderBy = Arrays.asList(cb.asc(root.get(Instructor_.id)),
                cb.asc(insIdProofJoin.get(IdProof_.proofNo)), cb.asc(insVehicleJoin.get(Vehicle_.vehicleNumber)),
                cb.asc(studentInsJoin.get(Instructor_.name)), cb.asc(studentVehicleJoin.get(Vehicle_.vehicleNumber)),
                cb.asc(vehicleDocumentJoin.get(Document_.name)));

        // prepare query
        cq.select(selection).where(where).orderBy(orderBy);
        DataPrinters.listDataPrinter.accept(queryExecutor.fetchListForCriteriaQuery(cq));

    }

Answer 3

我喜欢这种方法，因为它既简单又干净：

    String getCompaniesIdAndName = " select "
            + " c.id as id, "
            + " c.name as name "
            + " from Company c ";

    @Query(value = getCompaniesWithoutAccount)
    Set<CompanyIdAndName> findAllIdAndName();

    public static interface CompanyIdAndName extends DTO {
        Integer getId();

        String getName();

    }

Answer 4

您可以根据此类映射另一个实体（您应该使用实体名称来区分这两个），第二个实体将是dto（不要忘记dto has design issues）。你应该将第二个定义为readonly并给它一个好名字，以便明确这不是一个普通的实体。顺便说一下，只选择几列称为投影，所以google将更容易。

替代方案 - 您可以使用所需的字段列表创建命名查询（将它们放在选择中）或使用带投影的条件

Answer 5

您可以为此使用multiselect功能。

   CriteriaBuilder cb=session.getCriteriaBuilder();
            CriteriaQuery<Object[]> cquery=cb.createQuery(Object[].class);
            Root<Car> root=cquery.from(User.class);
            cquery.multiselect(root.get("id"),root.get("Name"));
            Query<Object[]> q=session.createQuery(cquery);
            List<Object[]> list=q.getResultList();
            System.out.println("id        Name");
            for (Object[] objects : list) {
                System.out.println(objects[0]+"        "+objects[1]);
             }

冬眠5支持此功能。createCriteria在冬眠的其他版本中已弃用。因此，您可以改用criteria builder。

Hibernate Criteria查询以获取特定列

5 个答案: