休眠条件查询以获取特定列

java mysql hibernate hibernate-criteria

2022-08-31 17:49:36

我在代码中使用了条件查询。它总是点火select * from ...

相反，我想忽略查询中的一列（字段），因为该字段以字节为单位存储了大量数据。这导致了性能问题。

任何人都可以对此给出一个想法吗？

一些更新

我在查询中添加了一个投影，它创建了一个查询，例如...

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 ?

现在的问题是.. 和相同的误差y8_，y5_意味着所有接近的地方，它给出了一个错误。Unknown column 'y4_' in 'where clause'

我把它修改为查询，就像...

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 ?

它奏效了。但是我不知道如何在HQL中修改它？

答案 1

使用“投影”可以指定要返回的列。

例

SQL 查询

SELECT user.id, user.name FROM user;

休眠替代方案

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();

答案 2

您可以使用 JPQL 和 JPA 标准 API 进行任何类型的 DTO 投影（仅将选定的列映射到 DTO 类）。查看下面的代码片段，这些代码片段显示了如何有选择地选择各种列，而不是选择所有列。这些示例还演示如何从联接多个列中选择各种列。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 code ：

@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));

    }