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I have a list of object which contain 10000 records i am trying to split that records in each of 10,

But somehow it is not working.. can someone have a look

@Query("select a.applicantid,coalesce(to_char(a.createdon,'yyyy-MM-dd'),to_char(filing_date,'yyyy-MM-dd')) as dt1, \r\n" + 
        "coalesce(c.companyname,i.InstituteName,(u.firstname||' '||u.lastname),\r\n" + 
        "u.firstname) ,a.c_denomination,cc.crop_common_name,cs.crop_botanical_name,\r\n" + 
        "a.id,aps.status,a.cropid, \r\n" + 
        "(select mv.varietytype from VarietyType mv where mv.id= a.varirtytypeid),\r\n" + 
        "(select sv.subvarietytype from SubVarietyType sv,VarietyType mvr \r\n" + 
        " where a.subvarietytypeid = sv.id and mvr.id= sv.varietyid),a.formtype,mcg.crop_group \r\n" + 
        " from Applications a left join ApplicantRegistration ap on \r\n" + 
        " a.applicantid = ap.id left join CompanyRegistration c on ap.companyid = c.id \r\n" + 
        " left join InstitutionRegistration i on ap.institutionid = i.id \r\n" + 
        " left join Crops cc on a.cropid = cc.id left join CropSpecies cs \r\n" + 
        " on a.cropspeciesid =cs.id left join InternalUser u on ap.id = u.applicantid \r\n" + 
        " left join ApplicationStatus aps on a.application_current_status = aps.id "
        + "left join CropGroup mcg on cc.cropgroupid = mcg.id order by a.id desc")
       List<Object[]> getapplication_adminview();



List<Object[]> admin_viewapplication=applicationrepository.getapplication_adminview();
int pageNumber = 0;
int size = 10;
Pageable pageable = PageRequest.of(pageNumber, size); // object of pageable
Page<Object> pages = new PageImpl(admin_viewapplication, pageable, admin_viewapplication.size());
List<Object> lpage = pages.getContent(); // here i am getting the lpage size as 10000 but as i enter pageable as of size 10  i am expecting 10 results only

where i am going wrong in this ? if i am trying to add pagable object to query and run the code i will get the following error:

Cannot create TypedQuery for query with more than one return using requested result type [java.lang.Long]; nested exception is java.lang.IllegalArgumentException: Cannot create TypedQuery for query with more than one return using requested result type [java.lang.Long]

Page just represents one page of data . So page.getContent() only return all data in one page which is specified through constructor when you create this page instance . It has nothing to do with splitting the data in a page.

If you want to split a list , use Lists from Guava is the simplest way to go :

List<List<Object>> splittedList = Lists.partition(list, 10);

If you want to do pagination which split all the data stored in the database into different smaller pages , split it at the database level rather than getting the whole list to the memory to split which will be very inefficient when the entire list is large. See this for how to split it at the database level by declaring Pageable in the query method.

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3 回答 3

1

Page只代表一页数据。因此，page.getContent()仅返回创建此页面实例时通过构造函数指定的一页中的所有数据。它与拆分页面中的数据无关。

如果要拆分列表，使用ListsfromGuava是最简单的方法：

List<List<Object>> splittedList = Lists.partition(list, 10);

如果要进行分页，将存储在数据库中的所有数据拆分为不同的较小页面，请在数据库级别进行拆分，而不是将整个列表放到内存中进行拆分，这在整个列表很大时效率非常低。有关如何通过在查询方法中声明来在数据库级别拆分它，请参阅this 。Pageable

于 2020-06-20T13:07:13.537 回答
0

We can use PagedListHolder which can change the list in pages and we can than fetch a page by setting it's page size and page.

PagedListHolder<Object> page = new PagedListHolder(admin_viewapplicationpage);
      page.setPageSize(50); // number of items per page
      page.setPage(0);      // set to first page

      int totalPages = page.getPageCount(); //  gives the totalpages according to the main list
      
      List<Object> admin_viewapplication = page.getPageList();  // a List which represents the current page which is the sublist
于 2020-06-20T15:23:14.147 回答
0

the following tutorial helped me -> https://www.baeldung.com/spring-data-jpa-query

At this point 4.3. Spring Data JPA Versions Prior to 2.0.4

VERY IMPORTANT to add \ n-- #pageable \ n

Without this I was wrong

Also the pagination setting must be without ordering

PageRequest paginaConf = new PageRequest ((param1 - 1)
                                                 , param2);

Finally to convert the Page <Object []>

  Page <Object []> list = myQueryofRepo ();
         List <XXXModel> lstReturn = myConversor (list.getContent ());
         Page <XXXModel> ret = new PageImpl <XXXModel> (lstReturn, pageConf, param2);
于 2021-04-21T05:57:15.657 回答