Django中多对多建表,查询方式

Django中多对多查询方式

from django.db import models

class Goods(models.Model):#商品
    g_name = models.CharField(max_length=20)
    g_price = models.DecimalField(max_digits=5, decimal_places=2)
    gc = models.ForeignKey("Category", null=True, on_delete=models.SET_NULL)#gc为外键,类别表为母表

class Category(models.Model):#类别
    c_name = models.CharField(max_length=20)


class Store(models.Model):#商家
    s_name = models.CharField(max_length=30)
    s_detail = models.TextField(blank=True, null=True)
    sc = models.ManyToManyField("Category")#与类别表进行多对多关联

多对多增删改查同时也适用一对多,一对一,修改少量参数即可

1.增
添加商家
Store.objects.create(s_name="商家A", s_detail="物美价廉,抄底折扣。。。。")
Out[2]: <Store: Store object>

Store(s_name="商家B", s_detail="大促销").save()

添加类别
Category.objects.create(c_name="电脑整机")
<Category: Category object>

Category(c_name="文具耗材").save()

增与改(增添子表或母表数据参照一对一的增,多对多重点在于关系表的对应关系变更)

创建商家C添加全部分类
Store.objects.create(s_name="商家C").sc.add(*(Category.objects.all()))#如果商户已存在则把create改成get

store = Store.objects.get(s_name="商家C")
store.sc=(Category.objects.all())
store.save()


创建商家D添加指定分类
store = Store.objects.create(s_name="商家D")
category = Category.objects.filter(c_name__in=["电脑整机","文具耗材"])#单个改成get,全部改成all
store.sc.add(*category)#add是追加模式
store.sc.clear()#清空此商家的商品

#让指定商品分类添加指定的商家,反向查询
store = Store.objects.create(s_name="商家E")
category = Category.objects.get(c_name="电脑整机")
category.store_set.add(store)
效果与上面一样

让所有商家都添加这个分类
stores = Store.objects.all()
category = Category.objects.get(c_name="电脑整机")
category.store_set.add(*stores)

category.store_set.clear()#让所有商家去除这个分类
category.store_set.all().delete()#是删除store_set的所有商家
#只有子表才有"子表名小写_set"的写法,得到的是一个QuerySet集合,后边可以接.add(),.remove(),.update(),.delete(),.clear()

2.查

(Store.objects.get(s_name="商家C")).sc.all()
<QuerySet [<Category: Category object>, <Category: Category object>]>

Category.objects.filter(store__s_name="商家C")
<QuerySet [<Category: Category object>, <Category: Category object>]>

#查找指定商家下面的所有分类
Store.objects.get(s_name="商家C").sc.all()#写法:子表对象.子表多对多字段.过滤条件(all()/filter())
<QuerySet [<Category: Category object>, <Category: Category object>]>

反向查询
Category.objects.filter(store__s_name="商家C")
Out[25]: <QuerySet [<Category: Category object>, <Category: Category object>]>#母表对象.filter(子表表名小写__子表字段名="过滤条件")

从分类查询,查看那些商家里面发布指定的某一个分类
(Category.objects.get(c_name="电脑整机")).store_set.all()
<QuerySet [<Store: Store object>, <Store: Store object>]>

Store.objects.filter(sc=Category.objects.get(c_name="电脑整机"))
<QuerySet [<Store: Store object>, <Store: Store object>]>

Store.objects.filter(sc__c_name="电脑整机")#filter(子表外键字段__母表字段='过滤条件')
<QuerySet [<Store: Store object>, <Store: Store object>]>

Store.objects.filter(sc=category)##filter得到QuerySet,写法:filter(子表外键字段=母表主键对象),此处和一对多略有不同,是子表外键字段而不是外键字段_母表主键
<QuerySet [<Store: Store object>, <Store: Store object>]>

3.删

让指定商家清空分类
s = Store.objects.get(s_name="商家C")
c = Category.objects.all()
s.sc = ""
s.save()

s=Store.objects.get(s_name="商家C")
c = Category.objects.all()
s.sc.remove(*c)

s = Store.objects.get(s_name="商家C")
s.sc.clear()

删除母表与子表关联关系
让所有商家去掉指定分类

s = Store.objects.all()
c = Category.objects.get(c_name="电脑整机")
c.store_set.remove(*s)

c = Category.objects.get(c_name="电脑整机")
c.store_set.clear()

#删除商家子表数据
删除所有指定分类的全部商家

c=Category.objects.get(c_name="电脑整机")
c.store_set.all().delete()

删除所有商家
Store.objects.all().delete()

猜你喜欢

转载自blog.csdn.net/ITcainiaoyizhan/article/details/87256498
0条评论
添加一条新回复