模型基本关系

class School(models.Model):   #“一方”模型

        name = models.CharField(max_length=30)
        address = models.CharField(max_length=30)
        history = models.TextField(null=True)

class Student(models.Model):
        name = models.CharField(max_length=20)
        age = models.InterField()
        score = models.FloatField()
        sex = models.CharField(max_length=10)
        school = models.ForeignKey(School,on_delete=models.CASCADE)

#添加学校对象（“一”方模型）
school1 = School.objects.create(name=‘清华大学‘，address=‘北京海淀区’)

school2 = School.objects.create(name=‘北京大学‘，address=‘北京‘，history=‘北京大学是一所知名大学‘)

school3 = School.objects.create(name=‘西安交通大学‘，address=‘西安‘，history=‘西安交大是一所很好的大学‘)

#通过外键类属性关联

stu1 = Student.objects.create(name=‘张三‘，age=20,score=93,sex=‘男‘，school = School1) 

#两个学生都上id为3的学校

stu3 = Student.objects.careate(name=‘李志‘，age=40,score=89,sex=‘男‘，school_id=3)

stu4 = Student.objects.careate(name=‘阿玛尼‘，age=35,score=89,sex=‘女‘，school_id=3)

#查询1号学校所有的学生：
school = School.objects.get(id=1)
students = school.student_set.all()

#查询5号学生对应的学校：
student = Student.objects.get(id=5)
school = student.school

class Person(models.Model):
        name = modles.CharField(max_length=20)
        age = models.IntergerField()
        sex = models.CharField(max_length=10)


class Card(models.Model):
        cardno = models.CharField(max_length=20,unique=True) #卡号类属性
        color = models.CharField(max_length=10)
        person = models.OneToOneField(Person,on_delete=models.CASCADE)#使用OneToOneField进行‘一对一’关联

　　#创建人对象
　　per = Person(name=‘张三‘，age=20,sex=‘男‘)

　　per.save()

　　#通过Card类的person属性关联

　　card = Card(cardno=‘zs123456‘,color=‘绿卡‘,person=per)

　　card.save()

　　per1 = Person(name=‘李四‘,age=22,sex=‘男‘)

　　per1.save()

　　card1 = Card.objects.create(cardno=‘ls123456‘,color=‘黄色‘,person_id=per1.id)

　　#查询3号卡关联的人

　　card = Card.objects.get(id=3)

　　per = card.person # 使用关联的类属性查询

#查询1号人的卡：

per1 = Person.objects.get(id=1)

card1 = per1.card  # 使用对方模型类名的小写

from django.db import models

class Member(models.Model):   # 成员模型
    name = models.CharField(max_length=20)
    age = models.IntegerField()
    sex = models.CharField(max_length=10)

    def __str__(self):
        return self.name

class Community(models.Model):  # 社团模型
    name = models.CharField(max_length=20)
    buildtime = models.DateField()
    members = models.ManyToManyField(Member,through="Relation")

    def __str__(self):
        return self.name

class Relation(models.Model):
    member = models.ForeignKey(Member,on_delete=models.CASCADE)
    community = models.ForeignKey(Community,on_delete=models.CASCADE)
    join_reason = models.CharField(max_length=100)

创建Member对象：
member1 = Member.objects.create(name=‘马小跳‘,age=20,sex=‘男‘)

member2 = Member.objects.create(name=‘李丽丽‘,age=25,sex=‘女‘)
member3 = Member.objects.create(name=‘黄大牛‘,age=35,sex=‘男‘)


创建Community对象：
community1 = Community.objects.create(name=‘天涯吉他社‘,buildtime=date(2016,6,6))

community2 = Community.objects.create(name=‘读书会‘,buildtime=date(2017,10,1))
 community3 = Community.objects.create(name=‘瑜伽协会‘,buildtime=date(2008,9,3))

创建Relation关系对象，通过实例化对象关联：
r1 = Relation.objects.create(member=member2,community=community1,join_reason=‘好玩‘)

通过外键值关联：
r2 = Relation.objects.create(member_id=member3.id,community_id=community1.id,join_reason=‘交朋友‘)

查询3号社团所有的成员：
方式一：借助中间模型查询：
community = Community.objects.get(id=3)
relations = Relation.objects.filter(community=community)

 for r in relations:
      print(r.member)

方式二：借助关联的类属性直接查询

all_members = community.members.all()
for m in all_members:
     print(m)

查询1号成员参加的社团：
member1 = Member.objects.get(id=1)
all_community = member1.community_set.all()
for c in all_community:
     print(c)