Django 多对多 关系

• 多对多，本意就是多个一对多的关系

• 定义多对多 ManyToManyField 字段

  from django.db import models
  
  # 学生类
  class Student(models.Model):
      name = models.CharField(max_length=32)
  
  # 老师类
  class Teacher(models.Model):
      name = models.CharField(max_length=32)
      students = models.ManyToManyField(to='Student',related_name='stu')

• 多对多添加

  • 添加一条记录

  # 老师选择学生
  teacherobj = models.Teacher.objects.filter(id=1).first()
  studentobj = models.Student.objects.filter(id=1).first()
  teacherobj.students.add(studentobj)
  return Response('ok')

  # 学生选择老师
  studentobj = models.Student.objects.filter(id=1).first()
  teacherobj = models.Teacher.objects.filter(id=2).first()
  studentobj.stu.add(teacherobj)
  return Response('ok')

  • 添加多条记录

  # 老师选择多名学生
  teacherobj = models.Teacher.objects.filter(id=3).first()
  teacherobj.students.add(*[1,2,3,4])
  teacherobj.save()

  # 学生选择多名老师
  studentobj = models.Student.objects.filter(id=2).first()
  studentobj.stu.add(*[3,4])
  studentobj.save()

  • 添加不重复的记录

  # 老师选择多名学生
  teacherobj = models.Teacher.objects.filter(id=3).first()
  teacherobj.students.set(*[1,2,3,4])
  teacherobj.save()

  # 学生选择多名老师
  studentobj = models.Student.objects.filter(id=2).first()
  studentobj.stu.set(*[3,4])
  studentobj.save()

• 多对多查询

  # 查询老师有多少名学生
  teacherobj = models.Teacher.objects.filter(id=3).first()
  stuobj = teacherobj.students.all()

  # 查询学生有多名老师
  studentobj = models.Student.objects.filter(id=2).first()
  teacherobj = studentobj.stu.all()

• 多对多更新

  # 老师批量换学生
  teacherobj = models.Teacher.objects.filter(id=3).first()
  teacherobj.students.set([1,2,3,4])

  # 学生批量换老师
  studentobj = models.Student.objects.filter(id=3).first()
  studentobj.stu.set([1,2,3,4])

• 多对多删除

  # 老师删除一个学生
  teacherobj = models.Teacher.objects.filter(id=3).first()
  studentobj = models.Student.objects.filter(id=2).first()
  teacherobj.students.remove(studentobj)

  # 学生删除一个老师
  studentobj = models.Student.objects.filter(id=3).first()
  teacherobj = models.Teacher.objects.filter(id=4).first()
  studentobj.stu.remove(teacherobj)
  studentobj.save()

  # 老师删除所有学生
  teacherobj = models.Teacher.objects.filter(id=1).first()
  teacherobj.students.clear()
  teacherobj.save()

  # 学生删除所有老师
  studentobj = models.Student.objects.filter(id=3).first()
  studentobj.stu.clear()
  studentobj.save()