Django ContentType组件详解

from django.db import models
class Appliance(models.Model):
    """
    家用电器表
    id name
    1   冰箱
    2   电视
    3   洗衣机
    """
    name = models.CharField(max_length=64)
class Food(models.Model):
    """
    食物表
    id name
    1  面包
    2  牛奶
    """
    name = models.CharField(max_length=32)
class Fruit(models.Model):
    """
    水果表
    id  name
    1   苹果
    2   香蕉
    """
    name = models.CharField(max_length=32)
class Coupon(models.Model):
    """
    优惠券表
    id  name    appliance_id    food_id     fruit_id
    1   通用优惠券   null            null        null
    2   冰箱折扣券   1               null        null
    3   电视折扣券   2               null        null
    4   苹果满减卷   null            null        1
    """
    name = models.CharField(max_length=32)
    appliance = models.ForeignKey(to="Appliance", null=True, blank=True)
    food = models.ForeignKey(to="Food", null=True, blank=True)
    fruit = models.ForeignKey(to="Fruit", null=True, blank=True)

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation

class Food(models.Model):
    """
    id      title
    1       面包
    2       牛奶
    """
    title = models.CharField(max_length=32)
    # 不会生成coupons字段,只用于反向查询
    coupons = GenericRelation(to="Coupon")

class Fruit(models.Model):
    """
    id      title
    1       苹果
    2       香蕉
    """
    title = models.CharField(max_length=32)

class Coupon(models.Model):
    title = models.CharField(max_length=32)
    # 第一步:在 model中定义ForeignKey字段,并关联到ContentType表
    content_type = models.ForeignKey(to=ContentType, on_delete=None)
    # 第二步:定义IntegerField字段,用来存储关联表中的主键
    object_id = models.IntegerField()
    # 第三步 不会生成字段传入上面两个字段的名字
    content_object = GenericForeignKey("content_type", "object_id")

class DemoView(APIView):
    def get(self, request):
        # 1.通过ContentType表找表模型
        content = ContentType.objects.filter(app_label="app1", model="food").first()
        # 获得表model对象 相当于models.app1
        model_class = content.model_class()
        ret = model_class.objects.all()
        print(ret)
        # 给面包创建一个优惠券
        food_obj = Food.objects.filter(id=1).first()
        Coupon.objects.create(title="面包九五折", content_type_id=8, object_id=1)
        Coupon.objects.create(title="双十一面包九折促销", content_object=food_obj)
        # 正向查询:根据优惠信息查询优惠对象
        coupon_obj = Coupon.objects.filter(id=1).first()
        content_obj = coupon_obj.content_object
        print(content_obj.title)
        # 反向查询:查询面包都有哪些优惠券
        coupons = food_obj.coupons.all()
        print(coupons[0].title)
        # 如果没定义反向查询
        content = ContentType.objects.filter(app_label="app1", model="food").first()
        result = Coupon.objects.filter(content_type=content, object_id=1).all()
        print(result[0].name)
        return Response("ContentType测试")