13 分页和shell命令行模式

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1.为什么先讲分页功能

先讲分页功能，新增或编辑博客内容在admin后台操作.png

2.快速添加新的博客

shell命令行模式下添加新博客：
- python manage.py shell，如下图所示：
  
  进入shell命令行模式.png
- for循环执行新增博客代码
添加一篇新的博客，涉及到Blog这个模型。因此在shell命令行模式下导入Blog这个模型。再用dir()方法来查看模型是否成功导入。如下图所示：

导入Blog博客模型.png
查询现有博客情况，如下图中的方法：

查询现有博客信息.png

3.模型新增对象

新增博客后的网页.png

>>> from blog.models import Blog
>>>
>>>
>>>
>>> Blog.objects.all()
<QuerySet [<Blog: <Blog: 长内容的博客>>, <Blog: <Blog: 人物介绍>>, <Blog: <Blog: Django简
介>>]
>>> Blog.objects.all().count()
3
>>> blog = Blog()


>>> Blog.objects.all()
<QuerySet [<Blog: <Blog: 长内容的博客>>, <Blog: <Blog: 人物介绍>>, <Blog: <Blog: Django简
介>>]>
>>> blog.title = "shell模式下的第一篇博客"
>>> blog.content = "这是一篇测试博客，233333333333333333333333333333333"
>>> from blog.models import BlogType
>>> dir()
['Blog', 'BlogType', '__builtins__', 'blog']

>>> BlogType.objects.all()
<QuerySet [<BlogType: Django>, <BlogType: 随笔>, <BlogType: 感悟>]>

>>> blog_type = BlogType.objects.all()[1]
>>> blog.blog_type = blog_type


>>> from django.contrib.auth.models import User
>>> User.objects.all()
<QuerySet [<User: CurryCoder>]>

>>> User.objects.all()
<QuerySet [<User: CurryCoder>]>
>>> user = User.objects.all()[0]
>>> blog.author = user


>>> blog.save()


>>> Blog.objects.all()
<QuerySet [<Blog: <Blog: 长内容的博客>>, <Blog: <Blog: 人物介绍>>, <Blog: <Blog: Django简
介>>, <Blog: <Blog: shell模式下的第一篇博客>>]>
>>> Blog.objects.all().count()
4
<!-- 查询blog对象的方法和属性 -->
>>> dir(blog)
['DoesNotExist', 'MultipleObjectsReturned', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setstate__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_check_column_name_clashes', '_check_field_name_clashes', '_check_fields', '_check_id_field', '_check_index_together', '_check_local_fields', '_check_long_column_names', '_check_m2m_through_same_relationship', '_check_managers', '_check_model', '_check_model_name_db_lookup_clashes', '_check_ordering', '_check_swappable', '_check_unique_together', '_do_insert', '_do_update', '_get_FIELD_display', '_get_next_or_previous_by_FIELD', '_get_next_or_previous_in_order', '_get_pk_val', '_get_unique_checks', '_meta', '_perform_date_checks', '_perform_unique_checks', '_save_parents', '_save_table', '_set_pk_val', '_state', 'author', 'author_id', 'blog_type', 'blog_type_id', 'check', 'clean', 'clean_fields', 'content', 'created_time', 'date_error_message', 'delete', 'from_db', 'full_clean', 'get_deferred_fields', 'get_next_by_created_time', 'get_next_by_last_updated_time', 'get_previous_by_created_time', 'get_previous_by_last_updated_time', 'id', 'last_updated_time', 'objects', 'pk', 'prepare_database_save', 'refresh_from_db', 'save', 'save_base', 'serializable_value', 'title', 'unique_error_message', 'validate_unique']
>>> blog.last_updated_time
datetime.datetime(2020, 5, 13, 13, 44, 45, 113603, tzinfo=<UTC>)

shell命令行模式下，快速添加大批量博客。具体效果如下如所示：

>>> for i in range(1,31):
...   blog = Blog()
...   blog.title = "for %s" % i
...   blog.content = "这是for循环生成的第%s篇博客" % i
...   blog.blog_type = blog_type
...   blog.author = user
...   blog.save()
...
...
>>> Blog.objects.all().count()
34

shell命令行模式下，快速添加大批量博客.png

4.分页器实现分页

通过上图我们可以看出，当一下显示所有的博客时。因此实现分页功能，更便于我们查看想要浏览的博客。

>>> del Blog  # 删除某个模型
>>> Blog
Traceback (most recent call last):
  File "<console>", line 1, in <module>
NameError: name 'Blog' is not defined
>>> exit()
>>> python manage.py shell
>>> dir()
['__builtins__']
>>> from django.core.paginator import Paginator
>>> from blog.models import Blog
>>> Blog.objects.all()
<QuerySet [<Blog: <Blog: 长内容的博客>>, <Blog: <Blog: 人物介绍>>, <Blog: <Blog: Django简
介>>, <Blog: <Blog: shell模式下的第一篇博客>>, <Blog: <Blog: for 1>>, <Blog: <Blog: for 2>
>, <Blog: <Blog: for 3>>, <Blog: <Blog: for 4>>, <Blog: <Blog: for 5>>, <Blog: <Blog: for 6>>, <Blog: <Blog: for 7>>, <Blog: <Blog: for 8>>, <Blog: <Blog: for 9>>, <Blog: <Blog: for 10>>, <Blog: <Blog: for 11>>, <Blog: <Blog: for 12>>, <Blog: <Blog: for 13>>, <Blog: <Blog: for 14>>, <Blog: <Blog: for 15>>, <Blog: <Blog: for 16>>, '...(remaining elements truncated)...']>
>>> blogs = Blog.objects.all()
>>> blogs.count()
34
>>> paginator = Paginator(blogs, 10)
<string>:1: UnorderedObjectListWarning: Pagination may yield inconsistent results with an unordered object_list: <class 'blog.models.Blog'> QuerySet.

出现上面的UnorderedObjectListWarning错误，这是由于没有设置分页后每一页按照什么顺序排序。因此打开blog目录下的models.py文件，在Blog类下添加Meta类如下所示：

from django.db import models
from django.contrib.auth.models import User

# Create your models here.

# 创建博文类型模型


class BlogType(models.Model):
    type_name = models.CharField(max_length=15)

    def __str__(self):
        return self.type_name

# 创建博文模型


class Blog(models.Model):
    title = models.CharField(max_length=50)
    # 一篇博文属于一种类型,因此博客通过外键关联到博文类型
    blog_type = models.ForeignKey(BlogType, on_delete=models.DO_NOTHING)
    content = models.TextField()
    author = models.ForeignKey(User, on_delete=models.DO_NOTHING)
    created_time = models.DateTimeField(auto_now_add=True)
    last_updated_time = models.DateTimeField(auto_now=True)

    def __str__(self):
        return "<Blog: %s>" % self.title
    <!-- 添加的新内容 -->
    class Meta:
        ordering = ['-created_time']

由于已经修改了Blog模型，所以要进行同步数据库。输入如下命令，如下图所示：

E:\Django\mysite_env\Scripts\mysite
$ python manage.py makemigrations
Migrations for 'blog':
  blog\migrations\0003_auto_20200513_2224.py
    - Change Meta options on blog

E:\Django\mysite_env\Scripts\mysite
$ python manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, blog, contenttypes, sessions
Running migrations:
  Applying blog.0003_auto_20200513_2224... OK

E:\Django\mysite_env\Scripts\mysite
$ python manage.py runserver
Performing system checks...

System check identified no issues (0 silenced).
May 13, 2020 - 22:24:47
Django version 2.0, using settings 'mysite.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CTRL-BREAK.

退出之前的shell命令行模型，重新进入shell命令行模式下，输入如下代码：

>>> from django.core.paginator import Paginator
>>> from blog.models import Blog
>>> blogs = Blog.objects.all()
>>> paginator = Paginator(blogs, 10)
>>> paginator
<django.core.paginator.Paginator object at 0x000000000469D978>
>>> dir(paginator)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_check_object_list_is_ordered', '_get_page', 'allow_empty_first_page', 'count', 'get_page', 'num_pages', 'object_list', 'orphans', 'page', 'page_range', 'per_page', 'validate_number']
>>> paginator.__doc__
>>> paginator.count
34
>>> paginator.num_pages
4
>>> paginator.page_range
range(1, 5)
>>>
>>> page1 = paginator.page(1)
>>> page1
<Page 1 of 4>
>>> dir(page1)
['__abstractmethods__', '__class__', '__contains__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', '__weakref__', '_abc_cache', '_abc_negative_cache', '_abc_negative_cache_version', '_abc_registry', 'count', 'end_index', 'has_next', 'has_other_pages', 'has_previous', 'index', 'next_page_number', 'number', 'object_list', 'paginator', 'previous_page_number', 'start_index']
>>> page1.count
<bound method Sequence.count of <Page 1 of 4>>
>>> help(page1.count)
Help on method count in module collections.abc:

count(value) method of django.core.paginator.Page instance
    S.count(value) -> integer -- return number of occurrences of value
>>>
>>> page1.object_list
[<Blog: <Blog: for 30>>, <Blog: <Blog: for 29>>, <Blog: <Blog: for 28>>, <Blog: <Blog: for 27>>, <Blog: <Blog: for 26>>, <Blog: <Blog: for 25>>, <Blog: <Blog: for 24>>, <Blog: <Blog: for 23>>, <Blog: <Blog: for 22>>, <Blog: <Blog: for 21>>]
>>> page1.object_list.count
<built-in method count of list object at 0x00000000046AFDC8>

分页器实现分页.png

5.分页的使用

前端页面：向后端服务器发送请求，请求打开具体的分页内容；
后端服务器：处理请求，返回具体分页内容响应请求；

例如，可以通过在浏览器中输入localhost:8000/blog/?page=1来访问第一页中的所有方法。因为前端通过url向服务器发送了GET请求，所以打开blog文件目录下的views.py文件，在blog_list()和blogs_with_type()函数中增加该请求对应的方法。views.py文件的内容如下：

from django.shortcuts import render_to_response, get_object_or_404
from django.core.paginator import Paginator
from .models import Blog, BlogType
# Create your views here.


def blog_list(request):
    blogs_all_list = Blog.objects.all()
    paginator = Paginator(blogs_all_list, 10)  # 每10篇进行一次分页
    page_num = request.GET.get('page', 1)  # 获取url的页码参数(GET请求)
    page_of_blogs = paginator.get_page(page_num)

    context = {}
    context['blogs'] = page_of_blogs.object_list
    context['page_of_blogs'] = page_of_blogs
    context['blog_types'] = BlogType.objects.all()
    return render_to_response('blog/blog_list.html', context)


def blog_detail(request, blog_pk):
    context = {}
    context['blog'] = get_object_or_404(Blog, pk=blog_pk)
    return render_to_response('blog/blog_detail.html', context)


def blogs_with_type(request, blog_type_pk):
    blogs_all_list = Blog.objects.all()
    paginator = Paginator(blogs_all_list, 2)  # 每2篇进行一次分页
    page_num = request.GET.get('page', 1)  # 获取url的页码参数(GET请求)
    page_of_blogs = paginator.get_page(page_num)

    context = {}
    blog_type = get_object_or_404(BlogType, pk=blog_type_pk)
    context['blog_type'] = blog_type
    context['blogs'] = Blog.objects.filter(blog_type=blog_type)
    context['blog_types'] = BlogType.objects.all()
    context['page_of_blogs'] = page_of_blogs
    return render_to_response('blog/blogs_with_type.html', context)

接着，修改blog文件目录下的templates文件夹下的blog_list.html模板文件，经过views.py处理请求后，返回新的结果给前端页面。blog_list.html修改后的结果如下所示：

{% extends 'base.html' %}
{# blog_list.html文件内容 #}
{# 页面标题 #}
{% block title %}我的网站{% endblock %}
{% block nav_blog_active %}active{% endblock %}

{% load staticfiles %}
{% block header_extends %}
    <link rel="stylesheet" href="{% static 'blog/blog.css' %}">
{% endblock %}

{# 页面内容 #}
{% block content %}
    <div class="container">
        <div class="row">
            <div class="col-xs-12 col-sm-8 col-md-9 col-lg-10">
                <div class="panel panel-default">
                    <div class="panel-heading">
                        {% block blog_list_title %}博客列表(一共有{{ page_of_blogs.paginator.count }}篇博客){% endblock %}
                    </div>
                    <div class="panel-body">
                        <!-- 下一行中的blogs来自于views.py中的context['blogs'] = Blog.objects.all() -->
                        {% for blog in blogs %}
                            <div class="blog">
                                <!-- 下一行中的blog.title来自于models.py中的title = models.CharField(max_length=50) -->
                                <h3><a href="{% url 'blog_detail' blog.pk %}">{{ blog.title }}</a></h3>
                                <p class="blog-info">
                                    <span class="glyphicon glyphicon-tag"></span><a href="{% url 'blogs_with_type' blog.blog_type.pk %}">{{ blog.blog_type }}</a> &nbsp&nbsp&nbsp
                                    <span class="glyphicon glyphicon-time"></span>{{ blog.created_time|date:"Y-m-d" }}
                                </p>
                                <p>{{ blog.content|truncatechars:120 }}</p>
                            </div>
                        {% empty %}
                           <div class="bog">
                                <h3>暂无博客，敬请期待</h3>
                           </div>
                        {% endfor %}
                    </div>
                </div>
                <!-- 此处使用了bootstrp组件中的分页代码 -->
                <div>
                    <ul class="pagination">
                        {# 上一页 #}
                        <li>
                            {% if page_of_blogs.has_previous %}
                                <a href="?page={{ page_of_blogs.previous_page_number }}" aria-label="Previous">
                                    <span aria-hidden="true">&laquo;</span>
                                </a>
                            {% else %}
                                <span aria-hidden="true">&laquo;</span>
                            {% endif %}

                        </li>

                        {# 全部页码 #}
                        {% for page_num in page_of_blogs.paginator.page_range %}
                            <li><a href="?page={{ page_num }}">{{ page_num }}</a></li>
                        {% endfor %}

                        {# 下一页 #}
                        <li>
                            {% if page_of_blogs.has_next %}
                                <a href="?page={{ page_of_blogs.next_page_number }}" aria-label="Next">
                                    <span aria-hidden="true">&raquo;</span>
                                </a>
                            {% else %}
                                <span aria-hidden="true">&raquo;</span>
                            {% endif %}
                        </li>
                    </ul>
                </div>



            </div>

            <div class="hidden-xs col-sm-4 col-md-3 col-lg-2">
                <div class="panel panel-default">
                    <div class="panel-heading">
                        博客分类
                    </div>
                    <div class="panel-body">
                        <ul class="blog-types">
                            {% for blog_type in blog_types %}
                                <li><a href="{% url 'blogs_with_type' blog_type.pk %}">{{ blog_type.type_name }}</a></li>
                            {% empty %}
                                <li>暂无分类</li>
                            {% endfor %}
                        </ul>
                    </div>
                </div>
            </div>
        </div>
    </div>

{% endblock %}