class Books(models.Model):nid = models.AutoField(primary_key=True)title = models.CharField(max_length=32)price = models.DecimalField(max_digits=8, decimal_places=2)  # 最大值: 999999.99pub_date = models.DateTimeField()  # django 要求必须存这种格式：2019-07-12publish = models.CharField(max_length=32)

# 增
## 方式一：
book = Book(title="python", price=123, pub_date="2019-9-22", publish="人民出版社")
book.save()## 方式二：推荐
book = Book.objects.create(title="python", price=123, pub_date="2019-9-22", publish="人民出版社")
print(book.title)
########### 添加书籍完整代码 ############
def addbook(request):   # get请求拿数据，post请求提交数据if request.method == "POST":title = request.POST.get('title')price = request.POST.get('price')pub_date = request.POST.get('pub_date')publish = request.POST.get('publish')Books.objects.create(title=title, price=price, pub_date=pub_date, publish=publish)return redirect(reverse("books"))else:  # get请求，请求的是添加书籍的表单页面，返回addbook.html页面给用户return render(request, "addbook.html", locals())

<!-- 书籍显示：完整的前端代码 -->
<!-- 书籍添加：完整的前端代码 -->
<h3>添加书籍</h3>
<div class="container"><div class="row"><div class="col-md-8 col-md-offset-2"><!--action在此处硬编码了，也可以利用反向解析实现：action="{% url 'addbook' %}"--><form action="/books/add/" method="post">   <!-- action 可以什么都不写，默认发到当前页面 -->{% csrf_token %}<div class="form-group"><label for="title">书籍名称</label><input type="text" class="form-control" id="title" placeholder="Title" name="title"></div><div class="form-group"><label for="price">价格</label><input type="text" class="form-control" id="price" placeholder="Price" name="price"></div><div class="form-group"><label for="pub_date">出版日期</label><input type="date" class="form-control" id="pub_date" placeholder="pub_date" name="pub_date"></div><div class="form-group"><label for="publish">出版社</label><input type="text" class="form-control" id="publish" placeholder="publish" name="publish"></div><button type="submit" class="btn btn-success pull-right">Submit</button></form></div></div>
</div>

# 查 -- 用的最多，最繁琐的
## 查询所有，结果为QuerySet（特殊的列表），可以for循环，可以切片 取数据
book_list = Book.objects.all()   # <QuerySet [<Books: Books object (1)>, <Books: Books object (2)>]>
## 条件查询
book_list= Book.objects.filter(price=100) # 返回的结果也是 QuerySet################# 完整的后端代码 #################
def books(request):# 查询所有book_list = Books.objects.all()return render(request, "books.html", {"book_list": book_list})

<!-- 书籍显示：完整的前端代码 -->
<h3>书籍列表</h3>
<div class="container"><div class="row"><div class="col-md-8 col-md-offset-2"><a href="/books/add/" class="btn btn-primary">添加书籍</a><table class="table table-striped table-hover">  <!-- striped为斑马线，hover为悬浮效果--><thead><tr><th>编号</th><th>书籍名称</th><th>价格</th><th>出版日期</th><th>出版社</th><th>操作</th></tr></thead><tbody>{% for book in book_list %}<tr><td>{{ book.nid }}</td><td>{{ book.title }}</td><td>{{ book.price }}</td><td>{{ book.pub_date|date:'Y-m-d'}}</td><td>{{ book.publish }}</td><td><a href="/books/edit/{{ book.nid }}" class="btn btn-warning btn-sm">编辑</a><!--href这里也是硬编码了，可以写成：href="{% url 'editbook' book.nid %}"--><!-- 如果有多个动态参数，用空格隔开即可 --><a href="/books/delete/{{ book.nid }}/" class="btn btn-danger btn-sm">删除</a></td></tr>{% endfor %}</tbody></table></div></div>
</div>

# 删 -- 想删谁，要先查出来，要用到查询
Book.objects.filter(nid=3).delete()   # 先找到要删除的结果（QuerySet），直接删除
Book.objects.get(nid=7).delete()   # model对象，找到自己，然后删除
####### 完整的后端代码 ########
def delbooks(request, delete_book_id):Books.objects.filter(nid=delete_book_id).delete()return redirect(reverse("books"))

# 改,与删的语法都很简单，关键点在于查，怎么能够将要操作的记录给查出来，语法如下
Books.objects.filter(nid=edit_book_id).update(price=120)  # http://127.0.0.1:8000/edit/9 就直接修改掉了
Books.objects.filter(price=111).update(publish="南京出版社")
return redirect("/books/")
############## 完整代码 ################
def editbooks(request, edit_book_id):if request.method == "GET":edit_book = Books.objects.filter(nid=edit_book_id)[0]return render(request, "editbook.html", {"edit_book": edit_book})else:title = request.POST.get('title')price = request.POST.get('price')pub_date = request.POST.get('pub_date')publish = request.POST.get('publish')Books.objects.filter(nid=edit_book_id).update(title=title, price=price, pub_date=pub_date, publish=publish)return redirect(reverse("books"))

<!-- 书籍编辑：完整的前端代码 -->
<a href="#">编辑书籍</a>
<div class="container"><div class="row"><div class="col-md-8 col-md-offset-2"><form action="" method="post">   <!-- action 可以什么都不写，默认发到当前页面 /books/edit/{{ edit_book.nid }} -->{% csrf_token %}<div class="form-group"><label for="title">书籍名称</label><input type="text" value="{{ edit_book.title }}" class="form-control" id="title" placeholder="Title" name="title"></div><div class="form-group"><label for="price">价格</label><input type="text" value="{{ edit_book.price }}" class="form-control" id="price" placeholder="Price" name="price"></div><div class="form-group"><label for="pub_date">出版日期</label><input type="date" value="{{ edit_book.pub_date|date:'Y-m-d'}}" class="form-control" id="pub_date" placeholder="pub_date" name="pub_date"></div><div class="form-group"><label for="publish">出版社</label><input type="text" value="{{ edit_book.publish }}" class="form-control" id="publish" placeholder="publish" name="publish"></div><button type="submit" class="btn btn-success pull-right">Submit</button></form></div></div>
</div>

<!-- 最新版本的 Bootstrap 核心 CSS 文件 -->
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css"integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<style>.container {margin-top: 65px;}
</style>

from django.contrib import admin
from django.urls import path, re_path
from book import viewsurlpatterns = [path('admin/', admin.site.urls),path('books/add/', views.addbook, name='addbook'),re_path('books/delete/(\d+)/', views.delbooks, name='delbooks'),re_path('books/edit/(\d+)/', views.editbooks, name='editbooks'),path('books/', views.books, name='books'),path('index/', views.index, name='index'),
]

# queryset
# get()方法应用场景（它的特性决定了它的使用场景很特别）
# 在上面的编辑书籍代码中的filter方法也可以换成get方法，因为用主键查询到的结果有且只有一个，不可能有重复的。又因为是编辑书籍，书籍也不可能不存在，所以这里用get方法很完美。
edit_book = Books.objects.get(nid=edit_book_id)   # 使用get方法，利用要编辑书籍的id，找到要编辑的书籍操作# 1 all()  返回 QuerySet
ret = Books.objects.all()  # <QuerySet [<Books: Python>, <Books: Shell>, <Books: GO>, <Books: ELK>]>
print(ret)
# 2 filter 返回 QuerySet
ret = Books.objects.filter(title='linux')  # <QuerySet [<Books: linux>]>
ret = Books.objects.filter(title='linux', price=23)  # <QuerySet [<Books: linux>]>
print(ret)
# 3 get() 返回查询到的 model对象，查到的结果有且只有一个才能正确返回，超过一个或不足一个就报错
ret = Books.objects.get(title='linux')
print(ret.title)   # model对象可以去点它的属性
# 4 first(),last()方法 QuerySet调用，返回model对象
fbook = Books.objects.all()[0]
fbook = Books.objects.all().first()
lbook = Books.objects.all().last()
# 5 exclude() 返回 QuerySet
ret = Books.objects.exclude(price=111)  # <QuerySet [<Books: Python>, <Books: ELK>, <Books: linux>]>
print(ret)
# 6 order_by() 返回 QuerySet
ret = Books.objects.all().order_by("price")
# 默认升序<QuerySet [<Books: linux>, <Books: ELK>, <Books: Python>, <Books: Shell>, <Books: GO>]>
ret = Books.objects.all().order_by("-price")
# 降序 <QuerySet [<Books: Shell>, <Books: GO>, <Books: Python>, <Books: ELK>, <Books: linux>]>
print(ret)

Book.objects.filter(price__in=[100,200,300])
Book.objects.filter(price__gt=100)
Book.objects.filter(price__gte=100)
Book.objects.filter(price__lt=100)
Book.objects.filter(price__range=[100,200])
Book.objects.filter(title__contains="python")
Book.objects.filter(title__icontains="python")
Book.objects.filter(title__startswith="py")
Book.objects.filter(pub_date__year=2012)