django 多对多关系的操作 包含映射表

图书馆的书，借书的学生为多对多关系

分为三张表，book ，stduent ，book_relation映射表

class Book:
name = models.CharField(max_length=100)
relation =models.ManyToManyField(student)

class Student(models.Model):
sname = models.CharField(max_length=100)

在自动生成数据库表的时候，会生成book表，student表，book_relation表，映射表名字的生成规则为models中class Book的名字加上manytomany的名字，即book+relation

插入数据

如果需要增加学生信息则student = Student(sname='1')

否则student = Student.objects.get(id=1)

book.relation.add(student)

book.save()

删除数据

student = Student.objects.get(id=1)

book.relation.remove(student)

book.save()

class Student(models.Model):
name = models.CharField(max_length=5)
cources = models.ManyToManyField(Course, through='StudentCourse')
class Course(models.Model):
name = models.CharField()
class StudentCourse(models.Model):
student = models.ForeignKey(Student)
course = models.ForeignKey(Course)
score=models.FloatField()