content_type

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation


class Electrics(models.Model):
    name = models.CharField(max_length=32)
    price = models.IntegerField(default=100)
    coupons = GenericRelation(to='Coupon')  # 用于反向查询，不会生成表字段

    def __str__(self):
        return self.name


class Foods(models.Model):
    name = models.CharField(max_length=32)
    price=models.IntegerField(default=100)
    coupons = GenericRelation(to='Coupon')

    def __str__(self):
        return self.name


class Clothes(models.Model):
    name = models.CharField(max_length=32)
    price = models.IntegerField(default=100)
    coupons = GenericRelation(to='Coupon')

    def __str__(self):
        return self.name





class Coupon(models.Model):
    """
    Coupon
        id    name                      content_type_id       object_id_id
    美的满减优惠券            9（电器表electrics）  3
    猪蹄买一送一优惠券        10                    2
    南极被子买200减50优惠券   11                    1
    """
    name = models.CharField(max_length=32)

    content_type = models.ForeignKey(to=ContentType,on_delete=models.CASCADE,null=True,blank=True) # step 1    #关联的那张表
    object_id = models.PositiveIntegerField(null=True,blank=True) # step 2   #关联的表中的字段
    content_object = GenericForeignKey('content_type', 'object_id') # step 3    方便查询  不会生成表字段

    def __str__(self):
        return self.name

 

#python终端打印
from django.contrib.contenttypes.models import ContentType
from app01.models import *
Electrics.objects.filter(id=1).first().coupons.all()
<QuerySet [<Coupon: 小天鹅满减券>, <Coupon: 小天鹅立减券>]>
el = Electrics.objects.filter(id=1).first()
el
<Electrics: 小天鹅洗衣机>

el.model_class()
Traceback (most recent call last):
  File "<input>", line 1, in <module>
AttributeError: 'Electrics' object has no attribute 'model_class'

el.__class__
<class 'app01.models.Electrics'>

Coupon.objects.filter(name="小天鹅立减券").first()
<Coupon: 小天鹅立减券>

Coupon.objects.filter(name="小天鹅立减券").first().content_object
<Electrics: 小天鹅洗衣机>

ContentType.objects.filter(app_label="app01",model="electrics").first()
<ContentType: electrics>



ContentType.objects.filter(app_label="app01",model="electrics").first().model_class()
<class 'app01.models.Electrics'>