Pagination 记忆线索

原文：https://docs.djangoproject.com/en/1.6/topics/pagination/ 

Pagination

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 django/core/paginator.py.

★ Django 分页

Example

Give 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:

★ 简单的示例，展示 Django 是如何工作的 

>>> 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()
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 callingcount(), 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 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.

★ 复杂一点的示例，通过view 和 template 展示如何分页 

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 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>

Paginator objects

The 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

Paginator. page( number)

Returns a Page object with the given 1-based index. Raises InvalidPage if the given page number doesn’t exist.

Attributes

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 callingobject_list.count(). If object_list has no count() method, then Paginator will fallback to usinglen(object_list). This allows objects, such as Django’s QuerySet, to use a more efficient count() method when available.

Paginator. num_pages

The total number of pages.

Paginator. page_range

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

InvalidPage exceptions

exception  InvalidPage

A base class for exceptions raised when a paginator is passed an invalid page number.

The Paginator.page() method raises an exception 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:

exception  PageNotAnInteger

Raised when page() is given a value that isn’t an integer.

exception  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

You usually won’t construct Page objects by hand – you’ll get them using Paginator.page().

class  Page( object_list,  number,  paginator)

A page acts like a sequence of Page.object_list when using len() or iterating it directly.

Methods

Page. has_next()

Returns True if there’s a next page.

Page. has_previous()

Returns True if there’s a previous page.

Page. has_other_pages()

Returns True if there’s a next or previous page.

Page. next_page_number()

Returns the next page number.

Changed in Django 1.5:

Raises InvalidPage if next page doesn’t exist.

Page. previous_page_number()

Returns the previous page number.

Changed in Django 1.5:

Raises InvalidPage if previous page doesn’t exist.

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 start_index() would return 3.

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 end_index() would return 4.

Attributes

Page. object_list

The list of objects on this page.

Page. number

The 1-based page number for this page.

Page. paginator

The associated Paginator object.