django 多对多操作

django 多对多操作

• 模型

  from django.db import models
  
  # 老师
  class Teacher(models.Model):
      name = models.CharField(max_length=32)
  
  # 学生
  class Student(models.Model):
      name = models.CharField(max_length=32)
      teachers = models.ManyToManyField(to='Teacher',on_delete=models.CASCADE)

• 查询

  # 通过老师查学生
  teacher = Teacher.objects.filter(id=1).first()
  students = teacher.student_set.all() # 获取所有学生信息
  
  # 通过学生查老师
  student = Student.objects.filter(id=2).first()
  teachers = student.teachers.all() # 获取所有老师的信息

• 添加

  # 学生选择老师
  t1 = Teacher.objects.filter(id=1).first()
  t2 = Teacher.objects.filter(id=2).first()
  t3 = Teacher.objects.filter(id=3).first()
  s1 = Student.objects.filter(id=4).first()
  s1.teacher.add(*[t1,t2,t3]) # 学生选择了三个老师
  
  # 老师选择学生
  s1 = Student.objects.filter(id=4).first()
  s2 = Student.objects.filter(id=5).first()
  t1.student_set.add(*[s1,s2]) # 老师选择了两个学生
  

• 清空

  # 通过老师清空
  t1 = Teacher.objects.filter(id=1).first()
  t1.student.clear() 
  
  # 通过学生清空
  s1 = Student.objects.filter(id=1).first()
  s1.teacher.clear()

• 删除指定数据

  t1 = Teacher.objects.filter(id=1).first()
  s1 = Student.objects.filter(id=1).first()
  # 以老师的角度删除与学生之间的关系
  t1.student_set.remove(s1)
  # 以学生的角度删除与老师之间的关系
  s1.teacher.remove(t1)