Improved Paging Support (Paginator)

[abdelgadir]

example client retrieving a paged result

    int pageSize = 20;
    String sortby = "firstname";
    String sortorder = "asc";
    int pageno = 1;

    YPage pageDef = new YPage();
    //jqGrid paging starts from 1 thus false parameter
    pageDef.setPageNumber(pageno, pagesize, false);
    if(!Strings.isNullOrEmpty(sortby)){
        pageDef.addOrder(sortby, YOrder.Sort.valueOf(sortorder.toUpperCase()));
    }

    //gets page 1 (first 20) of all employees that work for given company. returned page is sorted by 'firstname' in 'asc' order
    SearchResultList<Employee> employees = staffDao.findByCompanyId(getCompanyId(), pageDef);

    //gets page 2 (second 20) of all employees that work for given company. returned page is sorted by 'firstname' in 'asc' order
    pageDef.setPageNumber(pageno+1, pagesize, false);
    SearchResultList<Employee> employees = staffDao.findByCompanyId(getCompanyId(), pageDef);

[abdelgadir]

As shown in the above example, usage is very straightforward, you just specify which page you wish retrieved and the infrastructure takes care of the rest - you don't even need to specify the 'firstresultindex' and 'limit' parameters as the YPage works that out automatically.

Now having recently looked at django framework, I would probably implement the paging differently if i have to do it again.
Currently as in the above example, we need to pass the page definition with each query as in
staffDao.findByCompanyId(getCompanyId(), pageDef);

This means all method signatures will need to specify that parameter which is not nice.

Let me show you how djnago does paging to give an idea of what i am thinking.

django offers a Paginator class which takes a list of objects (or a set, or a tuple, or a queryset, basically any object with count() or len() method), plus the number of items you’d like to have on each page, and it gives you methods for accessing the items for each page. For example,

from django.core.paginator import Paginator
objects = [’john’, ’paul’, ’george’, ’ringo’]
p = Paginator(objects, 2)
p.count
4
p.num_pages
2
p.page_range
[1, 2]
page1 = p.page(1)
page1
<Page 1 of 2>
page1.object_list
[’john’, ’paul’]
page2 = p.page(2)
page2.object_list
[’george’, ’ringo’]
page2.has_next()
False
page2.has_previous()
True
page2.has_other_pages()
True
page2.next_page_number()
3
page2.previous_page_number()
1
page2.start_index() # The 1-based index of the first item on this page
3
page2.end_index() # The 1-based index of the last item on this page
4

It would be very nice and powerful if something similar could be included in this cdi query module.

[thomashug]

Functionality can be implemented by extending the QueryResult interface with paginator methods. The tricky part is to extract the count query - currently falling back to a persistence provider specific solution (needs to be optimized, only necessary for named queries).