django1/docs/topics/pagination.txt

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

.. module:: django.core.paginator
   :synopsis: Classes to help you easily manage paginated data.

Django provides a few classes that help you manage paginated data -- that is,
data that's split across several pages, with "Previous/Next" links. These
classes live in :file:`django/core/paginator.py`.

Example
=======

Give :class:`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
    >>> 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

    >>> 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.


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

Here's a slightly more complex example using :class:`Paginator` in a view to
paginate a queryset. We give both the view and the accompanying template to
show how you can display the results. This example assumes you have a
``Contacts`` model that has already been imported.

The view function looks like this::

    from django.core.paginator import Paginator, EmptyPage, PageNotAnInteger

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

        page = request.GET.get('page')
        try:
            contacts = paginator.page(page)
        except PageNotAnInteger:
            # If page is not an integer, deliver first page.
            contacts = paginator.page(1)
        except EmptyPage:
            # If page is out of range (e.g. 9999), deliver last page of results.
            contacts = paginator.page(paginator.num_pages)

        return render_to_response('list.html', {"contacts": contacts})

In the template :file:`list.html`, you'll want to include navigation between
pages along with any interesting information from the objects themselves::

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

    <div class="pagination">
        <span class="step-links">
            {% if contacts.has_previous %}
                <a href="?page={{ contacts.previous_page_number }}">previous</a>
            {% endif %}

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

            {% if contacts.has_next %}
                <a href="?page={{ contacts.next_page_number }}">next</a>
            {% endif %}
        </span>
    </div>

.. versionchanged:: 1.4
    Previously, you would need to use
    ``{% for contact in contacts.object_list %}``, since the ``Page``
    object was not iterable.


``Paginator`` objects
=====================

The :class:`Paginator` class has this constructor:

.. class:: Paginator(object_list, per_page, orphans=0, allow_empty_first_page=True)

Required arguments
------------------

``object_list``
    A list, tuple, Django ``QuerySet``, or other sliceable object with a
    ``count()`` or ``__len__()`` method.

``per_page``
    The maximum number of items to include on a page, not including orphans
    (see the ``orphans`` optional argument below).

Optional arguments
------------------

``orphans``
    The minimum number of items allowed on the last page, defaults to zero.
    Use this when you don't want to have a last page with very few items.
    If the last page would normally have a number of items less than or equal
    to ``orphans``, then those items will be added to the previous page (which
    becomes the last page) instead of leaving the items on a page by
    themselves. For example, with 23 items, ``per_page=10``, and
    ``orphans=3``, there will be two pages; the first page with 10 items and
    the  second (and last) page with 13 items.

``allow_empty_first_page``
    Whether or not the first page is allowed to be empty.  If ``False`` and
    ``object_list`` is  empty, then an ``EmptyPage`` error will be raised.

Methods
-------

.. method:: Paginator.page(number)

    Returns a :class:`Page` object with the given 1-based index. Raises
    :exc:`InvalidPage` if the given page number doesn't exist.

Attributes
----------

.. attribute:: Paginator.count

    The total number of objects, across all pages.

    .. note::

        When determining the number of objects contained in ``object_list``,
        ``Paginator`` will first try calling ``object_list.count()``. If
        ``object_list`` has no ``count()`` method, then ``Paginator`` will
        fallback to using ``object_list.__len__()``. This allows objects, such
        as Django's ``QuerySet``, to use a more efficient ``count()`` method
        when available.

.. attribute:: Paginator.num_pages

    The total number of pages.

.. attribute:: Paginator.page_range

    A 1-based range of page numbers, e.g., ``[1, 2, 3, 4]``.


``InvalidPage`` exceptions
==========================

The ``page()`` method raises ``InvalidPage`` if the requested page is invalid
(i.e., not an integer) or contains no objects. Generally, it's enough to trap
the ``InvalidPage`` exception, but if you'd like more granularity, you can trap
either of the following exceptions:

``PageNotAnInteger``
    Raised when ``page()`` is given a value that isn't an integer.

``EmptyPage``
    Raised when ``page()`` is given a valid value but no objects exist on that
    page.

Both of the exceptions are subclasses of ``InvalidPage``, so you can handle
them both with a simple ``except InvalidPage``.


``Page`` objects
================

.. class:: Page(object_list, number, paginator)

You usually won't construct :class:`Pages <Page>` by hand -- you'll get them
using :meth:`Paginator.page`.

.. versionadded:: 1.4
    A page acts like a sequence of :attr:`Page.object_list` when using
    ``len()`` or iterating it directly.

Methods
-------

.. method:: Page.has_next()

    Returns ``True`` if there's a next page.

.. method:: Page.has_previous()

    Returns ``True`` if there's a previous page.

.. method:: Page.has_other_pages()

    Returns ``True`` if there's a next *or* previous page.

.. method:: Page.next_page_number()

    Returns the next page number. Note that this is "dumb" and will return the
    next page number regardless of whether a subsequent page exists.

.. method:: Page.previous_page_number()

    Returns the previous page number. Note that this is "dumb" and will return
    the previous page number regardless of whether a previous page exists.

.. method:: Page.start_index()

    Returns the 1-based index of the first object on the page, relative to all
    of the objects in the paginator's list. For example, when paginating a list
    of 5 objects with 2 objects per page, the second page's :meth:`~Page.start_index`
    would return ``3``.

.. method:: Page.end_index()

    Returns the 1-based index of the last object on the page, relative to all of
    the objects in the paginator's list. For example, when paginating a list of
    5 objects with 2 objects per page, the second page's :meth:`~Page.end_index`
    would return ``4``.

Attributes
----------

.. attribute:: Page.object_list

    The list of objects on this page.

.. attribute:: Page.number

    The 1-based page number for this page.

.. attribute:: Page.paginator

    The associated :class:`Paginator` object.