初识Django之分页器Paginator

为什么要分页

分页功能是几乎所有的网站上都需要提供的功能，当你要展示的条目比较多时，必须进行分页，不但能减小数据库读取数据压力，也有利于用户浏览。

原生方法分页

在urls.py里urlpatterns中添加
path('getstudents/', views.get_students, name='get_students'),

views.py中添加get_students函数获取学生数量

def get_students(request):
  page = int(request.GET.get("page", 1))
  per_page = int(request.GET.get("per_page", 10))
  students = Student.objects.all()[per_page*(page-1): page*per_page]
  data = {
    "students": students
  }
  return  render(request, 'students.html', context=data)

通过访问http://127.0.0.1:8001/app/getstudents/?page=2&per_page=20可以看到分页效果

分页器Paginator

Django很贴心的为我们提供了一个Paginator分页工具。分页功能位于django.core.paginator模块。

API

Paginator提供包含一些对象的列表，以及你想每一页显示几条，比如每页5条、10条、20条、100条等等，它就会为你提供访问的一系列API方法，示例如下：

>>> from django.core.paginator import Paginator
>>> objects = ['john', 'paul', 'george', 'ringo']
>>> p = Paginator(objects, 2)  # 对objects进行分页，虽然objects只是个字符串列表，但没关系，一样用。每页显示2条。

>>> p.count   # 对象个数
4
>>> p.num_pages  # 总共几页
2
>>> type(p.page_range)  # `<type 'rangeiterator'>` in Python 2.
<class 'range_iterator'>
>>> p.page_range  # 分页范围
range(1, 3)

>>> page1 = p.page(1) # 获取第一页
>>> page1
<Page 1 of 2>
>>> page1.object_list # 获取第一页的对象
['john', 'paul']

>>> page2 = p.page(2)
>>> page2.object_list
['george', 'ringo']
>>> page2.has_next()  # 判断是否有下一页
False
>>> page2.has_previous()# 判断是否有上一页
True
>>> page2.has_other_pages() # 判断是否有其它页
True
>>> page2.next_page_number() # 获取下一页的页码
Traceback (most recent call last):
...
EmptyPage: That page contains no results
>>> page2.previous_page_number() # 获取上一页的页码
1
>>> page2.start_index() # 从1开始计数的当前页的第一个对象
3
>>> page2.end_index() # 从1开始计数的当前页最后1个对象
4

>>> p.page(0)  # 访问不存在的页面
Traceback (most recent call last):
...
EmptyPage: That page number is less than 1
>>> p.page(3) # 访问不存在的页面
Traceback (most recent call last):
...
EmptyPage: That page contains no results

实例

在urls.py里urlpatterns中添加
path('getstudentswithpage/', views.get_students_with_page, name='get_students_with_page')

views.py中添加getstudentswithpage函数获取学生数量

# 分页器
def get_students_with_page(request):

  page = int(request.GET.get("page", 1))
  per_page = int(request.GET.get("per_page", 10))

  students = Student.objects.all()
  paginator = Paginator(students, per_page)
  page_object = paginator.page(page)
  data = {
    "page_object": page_object,
    "page_range": paginator.page_range
  }
  return  render(request, 'students_with_page.html', context=data)

绘制students_with_page.html界面
包括前一页、下一页、边缘bug处理

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>students_with_page</title>
    <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet"
          integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3" crossorigin="anonymous">
</head>
<body>
<ul>
    {% for student in page_object.object_list %}
        <li>{{ student.s_name }}</li>
    {% endfor %}
</ul>

<nav aria-label="Page navigation">
    <ul class="pagination">
        {% if page_object.has_previous %}
            <li class="page-item">
                <a class="page-link"
                   href="{% url 'app:get_students_with_page' %}?page={{ page_object.previous_page_number }}"
                   aria-label="Previous">
                    <span aria-hidden="true">&laquo;</span>
                </a>
            </li>
        {% else %}
            <li class="disabled">
                <a class="page-link"
                   href="#"
                   aria-label="Previous">
                    <span aria-hidden="true">&laquo;</span>
                </a>
            </li>
        {% endif %}

        {% for page_index in page_range %}
            {% ifequal page_index page_object.number %}
                <li class="active"><a class="page-link"
                       href="{% url 'app:get_students_with_page' %}?page={{ page_index }}">{{ page_index }}</a></li>
                {% else %}
                <li><a class="page-link"
                       href="{% url 'app:get_students_with_page' %}?page={{ page_index }}">{{ page_index }}</a></li>
            {% endifequal %}
        {% endfor %}

        {% if page_object.has_next %}
            <li class="page-item">
                <a class="page-link"
                   href="{% url 'app:get_students_with_page' %}?page={{ page_object.next_page_number }}"
                   aria-label="Next">
                    <span aria-hidden="true">&raquo;</span>
                </a>

                {% else %}
            <li class="disabled">
                <a class="page-link" href="#" aria-label="Next">
                    <span aria-hidden="true">&raquo;</span>
                </a>
            </li>
        {% endif %}

    </ul>
</nav>
</body>
</html>