Django----ORM 基本操作的补偿

from django.db import models

# Create your models here.

class Classes(models.Model):
    ‘‘‘
    班级表
    ‘‘‘
    titile = models.CharField(max_length=32)
    m = models.ManyToManyField("Teacher")



class Teacher(models.Model):
    ‘‘‘
    老师表
    ‘‘‘
    name = models.CharField(max_length=32)

# 单表的增删改查
# 增
# Teacher.objects.create(name="root")
# obj=Teacher(name="root")
# obj.save()
# 查
# Teacher.objects.all()
# Teacher.objects.filter(id=1)
# Teacher.objects.filter(id=1,name="root")
# Teacher.objects.filter(id__gt=1)
# result=Teacher.objects.filter(id__gt=1).first()
#
# 删
# Teacher.objects.filter(id=1).delete()
#
# 改
# Teacher.objects.all().update(name="alex")
# Teacher.objects.filter(id=1).update(name="alex")





# class C2T(models.Model):
#     ‘‘‘
#     班级和老师之间的关系表
#     ‘‘‘
#     cid = models.ForeignKey(Classes)
#     tid = models.ForeignKey(Teacher)




#####################################多对多
‘‘‘
班级：
id   titile
1       1班
2       2班
3       3班
老师：
id  name
1    alex
2    dou
3    chou
4    lv
增加
obj1 = Classes.objects.filter(id=1).first()
obj1.m.add(2) # 2就是老师id
obj1.m.add([4,5]) # 4,5就是老师id


obj2 = Classes.objects.filter(id=2).first()
obj2.m.add(2) # 2就是老师id
obj2.m.add([4,5]) # 3,5就是老师id
删除
obj1.m.remove([4,5]) #删除 4，5老师
清空
obj2.m.clear() #删除 将班级id=2的老师全部删除
重置
obj2.m.set([2,3,4]) #将班级id=2的老师设置为id=[2,3,4]


把2班的所有老师列绝出来
obj3 = Class.objects.filter(id=2).first()  #得到2班
obj3.id
obj3.titile
ret = obj3.m.all()   #ret是一个列表，[老师2（id,name）,老师3（id,name）,老师4（id,name）]  


老师班级关系表 
id   班级id  老师id
1       1       2
4       2       2
5       2       3
6       2       4

‘‘‘




class Student(models.Model):
    ‘‘‘
    学生表
    ‘‘‘
    username = models.CharField(max_length=32)
    age = models.IntegerField()
    gender = models.BooleanField()
    cs = models.ForeignKey(Classes,on_delete=models.CASCADE,)

‘‘‘
id  username age  gender cs_id

增加
Student.objects.create(username="aa",age=12,gender="男",cs_id=1)
Student.objects.create(username="aa",age=12,gender="男",cs_id=Classes.objects.filter(id=1).first)
查看
ret = Student.objects.filter(id=1)
for item in ret:
    print(item.id)
    print(item.username)
    print(item.age)
    print(item.gender)
    print(item.cs_id)
    print(item.cs.id)
    print(item.cs.name)
删除
Student.objects.filter(id=1).delete()
Student.objects.filter(cs_id=1).delete()

cid = input("请输入班级ID")
Student.objects.filter(cs_id=cid).delete()

cname=input("请输入班级名称")
Student.objects.filter(cs__name=cname).delete()   //写filter条件的时候，用__来跨表

修改
Student.objects.filter(cs_id=1).update()

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