Django—模型对应关系（多对多）

目录

1. 模型
2. 增加
3. 删除
4. 正反向查询

---

1. 模型

   ---

   ;⼀个买家可以购买多件商品，⼀件商品可以被多个买家购买，买家和商品之间构成
   ;多对多关系，多对多关系必然会⽣成⼀张中间表：买家-商品表，记录商品和买家
   ;的关系，该表包含商品表主键和买家表的主键
   
   from django.db import models
   # Create your models here.
   class Buyer(models.Model):
    bname = models.CharField(max_length=30)
    level = models.IntegerField(default=1)
   class Goods(models.Model):
    gname = models.CharField(max_length=100)
    price = models.FloatField()
    buyer = models.ManyToManyField(Buyer) #这种写法⾃动⽣成第三张表，但
   我们⽆法直接控制
    def __str__(self):
    return self.gname +" "+ str(self.price)
   #⼿动创建中间表
   class Orders(models.Model):
    buyer =
   models.ForeignKey(Buyer,on_delete=models.CASCADE,db_column='bid')
    goods =
   models.ForeignKey('Goods',on_delete=models.CASCADE,db_column='gid')
    num = models.Integer(default=1)
   class Goods(models.Model):
    gname = models.CharField(max_length=100)
    price = models.FloatField()
    buyer = models.ManyToManyField(Buyer,through='Orders')

2. 增加

   ---

   def sellgoods(req):
    goods = Goods.objects.get(pk=randint(1,Goods.objects.count()))
    
   goods.buyer.add(Buyer.objects.get(pk=randint(1,Buyer.objects.count())
   ))
    goods.save()
    return HttpResponse("剁⼿成功")

3. 删除

   ---

    buyer = Buyer.objects.get(pk=13)
   goods = Goods.objects.filter(pk__lt=10)
   buyer.goods_set.clear() #删除所有商品
   buyer.goods_set.remove(Goods.objects.get(pk=2)) #删除指定商品

4. 正反向查询

   ---

   # 正向查询
   
   def findgoods_by_buyer(req):
    buyer = Buyer.objects.get(pk=13)
    res = buyer.goods_set.all()
    print(res)
    return HttpResponse("由买家查询商品")
   
   
   # 反向查询
   def findbuyer_by_goods(request):
    goods = Goods.objects.last()
    buyer = goods.buyer.all()
    print(buyer)
    return HttpResponse("由商品查询买家")