django学习之Pagination

　　django本身提供一些类来处理分页数据，这些类都在django/core/paginator.py里面。

　　paginator里面有两个重要的类：Paginator与Page.那就分别说说这两个类吧

class Paginator(object):
    def __init__(self, object_list, per_page, orphans=0, allow_empty_first_page=True):
        self.object_list = object_list
        self.per_page = int(per_page)
        self.orphans = int(orphans)
        self.allow_empty_first_page = allow_empty_first_page
        self._num_pages = self._count = None

    def validate_number(self, number):
        "Validates the given 1-based page number."
        try:
            number = int(number)
        except (TypeError, ValueError):
            raise PageNotAnInteger('That page number is not an integer')
        if number < 1:
            raise EmptyPage('That page number is less than 1')
        if number > self.num_pages:
            if number == 1 and self.allow_empty_first_page:
                pass
            else:
                raise EmptyPage('That page contains no results')
        return number

    def page(self, number):
        "Returns a Page object for the given 1-based page number."
        number = self.validate_number(number)
        bottom = (number - 1) * self.per_page
        top = bottom + self.per_page
        if top + self.orphans >= self.count:
            top = self.count
        return Page(self.object_list[bottom:top], number, self)

    def _get_count(self):
        "Returns the total number of objects, across all pages."
        if self._count is None:
            try:
                self._count = self.object_list.count()
            except (AttributeError, TypeError):
                # AttributeError if object_list has no count() method.
                # TypeError if object_list.count() requires arguments
                # (i.e. is of type list).
                self._count = len(self.object_list)
        return self._count
    count = property(_get_count)

    def _get_num_pages(self):
        "Returns the total number of pages."
        if self._num_pages is None:
            if self.count == 0 and not self.allow_empty_first_page:
                self._num_pages = 0
            else:
                hits = max(1, self.count - self.orphans)
                self._num_pages = int(ceil(hits / float(self.per_page)))
        return self._num_pages
    num_pages = property(_get_num_pages)

    def _get_page_range(self):
        """
        Returns a 1-based range of pages for iterating through within
        a template for loop.
        """
        return range(1, self.num_pages + 1)
    page_range = property(_get_page_range)

　　paginator是控制分页的类。主要方法有它的构造方法与page方法.

　　__init__(self,object_list,per_page,orphans=0,allow_empty_first_page=True):object_list是分页数据对象，per_page是每页最大的item数，orphans表示最后一页最小item的个数：如果最后一页item个数小于等于orphans，那么把最后一页的内容添加到前一页中，否则不会添加；allow_empty_first_page是是否允许第一页数据为空（目前我不清楚这个到底有什么作用）

　　page(self, number)：根据page的number返回第number的数据内容，它返回的是Page对象出PageNotAnInteger,EmptyPage异常

　　

　　Page是表示要展示的某页数据的对象，但是它同时拥有一个控制分页数据的Paginator对象。这个Paginator赋予了Page更多的功能

class Page(object):
    def __init__(self, object_list, number, paginator):
        self.object_list = object_list
        self.number = number
        self.paginator = paginator

    def __repr__(self):
        return '<Page %s of %s>' % (self.number, self.paginator.num_pages)

    def __len__(self):
        return len(self.object_list)

    def __getitem__(self, index):
        # The object_list is converted to a list so that if it was a QuerySet
        # it won't be a database hit per __getitem__.
        return list(self.object_list)[index]

    # The following four methods are only necessary for Python <2.6
    # compatibility (this class could just extend 2.6's collections.Sequence).

    def __iter__(self):
        i = 0
        try:
            while True:
                v = self[i]
                yield v
                i += 1
        except IndexError:
            return

    def __contains__(self, value):
        for v in self:
            if v == value:
                return True
        return False

    def index(self, value):
        for i, v in enumerate(self):
            if v == value:
                return i
        raise ValueError

    def count(self, value):
        return sum([1 for v in self if v == value])

    # End of compatibility methods.

    def has_next(self):
        return self.number < self.paginator.num_pages

    def has_previous(self):
        return self.number > 1

    def has_other_pages(self):
        return self.has_previous() or self.has_next()

    def next_page_number(self):
        return self.number + 1

    def previous_page_number(self):
        return self.number - 1

    def start_index(self):
        """
        Returns the 1-based index of the first object on this page,
        relative to total objects in the paginator.
        """
        # Special case, return zero if no items.
        if self.paginator.count == 0:
            return 0
        return (self.paginator.per_page * (self.number - 1)) + 1

    def end_index(self):
        """
        Returns the 1-based index of the last object on this page,
        relative to total objects found (hits).
        """
        # Special case for the last page because there can be orphans.
        if self.number == self.paginator.num_pages:
            return self.paginator.count
        return self.number * self.paginator.per_page

　　主要的几个方法，因为简单，这里就不解释了：

　　def has_next(self):
        return self.number < self.paginator.num_pages

    def has_previous(self):
        return self.number > 1

    def has_other_pages(self):
        return self.has_previous() or self.has_next()

    def next_page_number(self):
        return self.number + 1

    def previous_page_number(self):
        return self.number - 1

　　官网上有一个小例子，蛮简单的：

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})

　　在list.html里，你可以这样做：

{% 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>