==========
Pagination
==========

Django provides high-level and low-level ways to help you manage paginated data
-- that is, data that's split across several pages, with "Previous/Next" links.

The ``Paginator`` class
=======================

Under the hood, all methods of pagination use the
:class:`~django.core.paginator.Paginator` class. It does all the heavy lifting
of actually splitting a ``QuerySet`` into :class:`~django.core.paginator.Page`
objects.

Example
=======

Give :class:`~django.core.paginator.Paginator` a list of objects, 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::

    >>> from django.core.paginator import Paginator
    >>> objects = ['john', 'paul', 'george', 'ringo']
    >>> p = Paginator(objects, 2)

    >>> p.count
    4
    >>> p.num_pages
    2
    >>> type(p.page_range)
    <class 'range_iterator'>
    >>> p.page_range
    range(1, 3)

    >>> 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()
    Traceback (most recent call last):
    ...
    EmptyPage: That page contains no results
    >>> 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

    >>> p.page(0)
    Traceback (most recent call last):
    ...
    EmptyPage: That page number is less than 1
    >>> p.page(3)
    Traceback (most recent call last):
    ...
    EmptyPage: That page contains no results

.. note::

    Note that you can give ``Paginator`` a list/tuple, a Django ``QuerySet``,
    or any other object with a ``count()`` or ``__len__()`` method. When
    determining the number of objects contained in the passed object,
    ``Paginator`` will first try calling ``count()``, then fallback to using
    ``len()`` if the passed object has no ``count()`` method. This allows
    objects such as Django's ``QuerySet`` to use a more efficient ``count()``
    method when available.

Paginating a ``ListView``
=========================

:class:`django.views.generic.list.ListView` provides a builtin way to paginate
the displayed list. You can do this by adding a
:attr:`~django.views.generic.list.MultipleObjectMixin.paginate_by` attribute to
your view class, for example::

    from django.views.generic import ListView

    from myapp.models import Contact

    class ContactListView(ListView):
        paginate_by = 2
        model = Contact

This limits the number of objects per page and adds a ``paginator`` and
``page_obj`` to the ``context``. To allow your users to navigate between pages,
add links to the next and previous page, in your template like this:

.. code-block:: html+django

    {% for contact in page_obj %}
        {# Each "contact" is a Contact model object. #}
        {{ contact.full_name|upper }}<br>
        ...
    {% endfor %}

    <div class="pagination">
        <span class="step-links">
            {% if page_obj.has_previous %}
                <a href="?page=1">&laquo; first</a>
                <a href="?page={{ page_obj.previous_page_number }}">previous</a>
            {% endif %}

            <span class="current">
                Page {{ page_obj.number }} of {{ page_obj.paginator.num_pages }}.
            </span>

            {% if page_obj.has_next %}
                <a href="?page={{ page_obj.next_page_number }}">next</a>
                <a href="?page={{ page_obj.paginator.num_pages }}">last &raquo;</a>
            {% endif %}
        </span>
    </div>

.. _using-paginator-in-view:

Using ``Paginator`` in a view function
======================================

Here's an example using :class:`~django.core.paginator.Paginator` in a view
function to paginate a queryset::

    from django.core.paginator import Paginator
    from django.shortcuts import render

    from myapp.models import Contact

    def listing(request):
        contact_list = Contact.objects.all()
        paginator = Paginator(contact_list, 25) # Show 25 contacts per page.

        page_number = request.GET.get('page')
        page_obj = paginator.get_page(page_number)
        return render(request, 'list.html', {'page_obj': page_obj})

In the template :file:`list.html`, you can include navigation between pages in
the same way as in the template for the ``ListView`` above.
