十一、ContentType组件

11.1 模型

• models.py

  from django.db import models
  from django.contrib.contenttypes.models import ContentType
  from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation
  
  
  class Food(models.Model):
      """ 商品种类 """
      title = models.CharField(max_length=32)
      # 4. 和Coupon绑定外键关系，只用于反向查询，不生成字段
      coupons = GenericRelation(to="Coupon")
  
  ...
  
  class Coupon(models.Model):
      """ 优惠券 """
      title = models.CharField(max_length=32)
      # 1. 和ContentType绑定外键关系
      content_type = models.ForeignKey(to=ContentType, on_delete=models.CASCADE)
      # 2. 建立对象id
      object_id = models.IntegerField()
      # 3. 把object_id和object_id绑定外键关系，不生成字段
      content_object = GenericForeignKey("content_type", "object_id")
  
  

11.2 视图

• views.py

  from rest_framework.views import APIView
  from rest_framework.response import Response
  from .models import Food, Coupon
  from django.contrib.contenttypes.models import ContentType
  
  
  class DemoView(APIView):
  
      def get(self, request):
          # 1. 找到具体食物对象
          food_obj = Food.objects.filter(id=1).first()
  
          # 2. 创建食物优惠券：手动实现（不推荐）
          # Coupon.objects.create(title="面包九五折", content_type_id=8, object_id=1)
  
          # 2. 创建食物优惠券：Django内置方法实现
          Coupon.objects.create(title="面包九五折", content_object=food_obj)
  
          # 3.1 通过食物对象查询优惠券对象（反向查询GenericRelation）
          coupons = food_obj.coupons.all()
          # 3.2 通过优惠券对象查询食物对象（正向查询content_object）
          coupon_obj = Coupon.objects.filter(id=1).first()
          content_obj = coupon_obj.content_object
  
          # 4. 通过ContentType表找到表模型：app名 + 表名
          content = ContentType.objects.filter(app_label="demo", model="food").first()
          print(content)  # food
          # model_class()方法得到食物表模型，即food_obj
          model_class = content.model_class()
          ret = model_class.objects.all()
          print(ret)  # <QuerySet [..., ...]>
  
          return Response("ContentType测试")