Django ORM 常用增刪改查語法、API及示例

Django ORM 常用增刪改查語法、API及示例

Django ORM（Object-Relational Mapping）是Django框架中用于与数据库进行交互的模块。它提供了一种面向对象的方式来操作数据库，使得开发者可以更加方便地进行增删改查等操作。本文将详细介绍Django ORM的常用增删改查操作及其API，并给出详细的示例和注释。

1. 模型定义 (Models)

首先，我们需要定义一个模型类，该类继承自django.db.models.Model。模型类中的每个属性都对应数据库中的一个字段。

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)
    age = models.IntegerField()

    def __str__(self):
        return self.name

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)
    published_date = models.DateField()
    isbn = models.CharField(max_length=13)

    def __str__(self):
        return self.title

2. 序列化器 (Serializers)

为了将模型实例转换为JSON格式的数据，我们通常使用Django REST framework提供的序列化器。

from rest_framework import serializers
from .models import Author, Book

class AuthorSerializer(serializers.ModelSerializer):
    class Meta:
        model = Author
        fields = '__all__'

class BookSerializer(serializers.ModelSerializer):
    class Meta:
        model = Book
        fields = '__all__'

3. 增 (Create)

3.1 创建单个对象

# 创建一个新作者
new_author = Author(name='John Doe', age=45)
new_author.save()

3.2 使用序列化器创建对象

from rest_framework.renderers import JSONRenderer
from rest_framework.parsers import JSONParser
import io

data = {'name': 'Jane Doe', 'age': 30}
serializer = AuthorSerializer(data=data)
if serializer.is_valid():
    serializer.save()

4. 查 (Read)

4.1 查询所有对象

authors = Author.objects.all()
for author in authors:
    print(author.name, author.age)

4.2 查询单个对象

try:
    author = Author.objects.get(id=1)
    print(author.name, author.age)
except Author.DoesNotExist:
    print("Author not found")

4.3 使用序列化器查询对象

author = Author.objects.get(id=1)
serializer = AuthorSerializer(author)
json_data = JSONRenderer().render(serializer.data)
print(json_data)

5. 改 (Update)

5.1 更新单个字段

author = Author.objects.get(id=1)
author.age = 46
author.save()

5.2 更新多个字段

author = Author.objects.get(id=1)
author.name = 'John Smith'
author.age = 47
author.save()

5.3 使用序列化器更新对象

data = {'name': 'John Smith', 'age': 48}
author = Author.objects.get(id=1)
serializer = AuthorSerializer(author, data=data)
if serializer.is_valid():
    serializer.save()

6. 删 (Delete)

6.1 删除单个对象

author = Author.objects.get(id=1)
author.delete()

6.2 批量删除对象

Author.objects.filter(age__lt=30).delete()

7. 高级查询 (Advanced Queries)

7.1 过滤查询 (Filtering)

# 获取年龄大于40的作者
older_authors = Author.objects.filter(age__gt=40)
for author in older_authors:
    print(author.name, author.age)

7.2 排序查询 (Ordering)

# 按年龄升序排列作者
authors_sorted_by_age = Author.objects.order_by('age')
for author in authors_sorted_by_age:
    print(author.name, author.age)

7.3 聚合查询 (Aggregation)

from django.db.models import Avg, Max, Min, Count, Sum

# 计算平均年龄
average_age = Author.objects.aggregate(Avg('age'))['age__avg']
print(f"Average Age: {average_age}")

7.4 关联查询 (Related Lookups)

# 获取某本书的作者信息
book = Book.objects.get(id=1)
author_name = book.author.name
print(f"The author of the book is: {author_name}")

8. API视图 (API Views)

Django REST framework提供了一些通用的视图来处理常见的HTTP请求。以下是一个简单的例子，展示如何使用这些视图。

8.1 安装Django REST framework

首先，确保你已经安装了Django REST framework：

pip install djangorestframework

8.2 配置settings.py

在settings.py中添加rest_framework到INSTALLED_APPS：

INSTALLED_APPS = [
    ...,
    'rest_framework',
]

8.3 创建视图 (Views)

在views.py中创建视图：

from rest_framework import viewsets
from .models import Author, Book
from .serializers import AuthorSerializer, BookSerializer

class AuthorViewSet(viewsets.ModelViewSet):
    queryset = Author.objects.all()
    serializer_class = AuthorSerializer

class BookViewSet(viewsets.ModelViewSet):
    queryset = Book.objects.all()
    serializer_class = BookSerializer

8.4 配置URL路由 (URL Routing)

在urls.py中配置路由：

from django.urls import path, include
from rest_framework.routers import DefaultRouter
from .views import AuthorViewSet, BookViewSet

router = DefaultRouter()
router.register(r'authors', AuthorViewSet)
router.register(r'books', BookViewSet)

urlpatterns = [
    path('', include(router.urls)),
]

9. 总结

本文详细介绍了Django ORM的常用增删改查操作及其API，并通过示例展示了如何定义模型、序列化器以及如何使用视图和路由来处理HTTP请求。通过这些内容，你可以更好地理解和使用Django ORM来进行数据库操作。

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