When data cannot be displayed on one single Web page, you might have already heard about pagination or paging. TreeFrog provides such a function which divides into multiple Web pages. This technique is very common for many web applications on the internet.

TreeFrog provides a class for pagination with very basic functions. In order to use TreeFrog’s pagination ability you need to use the TPaginator class. The following example - written in ERB, but similar to Otama - will show you how to use pagination.

First of all, in the action of the controller class we will retrieve information about the current displaying page number by using query arguments. Then we get a list of models that correspond to that page number and pass them to the view.

int current = httpRequest().queryItemValue("page", "1").toInt();
int totalCount = Blog::count();

// Display up to ten items per page. The argument '5' specifies the number of pages
// to show ‘around’ the current page on a pagination bar, and should be an odd number
TPaginator pager(totalCount, 10, 5);
pager.setCurrentPage(current);  // Set the page number that is supposed to be displayed

// Obtain the corresponding items and add them to the view
QList<Blog> blogList = Blog::getBlogs( pager.itemCountPerPage(), pager.offset() );

Now, let’s have a look at the view.
It is a good technique to use a partial template when you want to display page numbers.
In the following example, we used the passed TPaginator object to draw the page numbers and their respective links. For each link, the urlq() method creates the URL and the specified query arguments to the current action for you.

Using template: views/partial/pagination.erb

<%#include <TPaginator> %>
<% tfetch(TPaginator, pager); %>

<div class="pagination">
  <%== linkToIf(pager.hasPrevious(), "Prev", urlq("page=" + QString::number( pager.previousPage() ))) %>

  <% for (QListIterator<int> i(pager.range()); i.hasNext(); ) {
      int page =; %>
      <%== linkToIf((page != pager.currentPage()), QString::number(page), urlq("page=" + QString::number(page))); %>
  <% } %>

  <%== linkToIf(pager.hasNext(), "Next", urlq("page=" + QString::number( pager.nextPage() ))) %>

Rendering a partial template is rather simple. Use the following renderPartial() method to achieve this:

<%== renderPartial("pagination") %>

The passing argument “pagination” is the name of the template you want to include. Furthermore, this template draws a list of models passed from the controller. For more details about rendering templates, please refer to the generator which generates templates such as index, show etc.

Next is the acquisition of the model.
To obtain a list of applicable models, you can issue a query with the LIMIT and OFFSET parameters from the database. Depending on your requirements, you may need to specify a WHERE or to sort the obtaining models.

Because such SQL queries are commonly used, the following TreeFrog Framework utility function requires not much code.

QList<Blog> Blog::getBlogs(int limit, int offset)
    return tfGetModelListByCriteria<Blog, BlogObject>(TCriteria(), limit, offset);

Please refer the API Reference page for more details about the model utility.

Since pagination is not that difficult, you can also try to challenge the implementation without using the TPaginator class at all.