Django—模型对应关系（一对一）

• 一对一模型

  ---

  #⼀个学⽣有⼀个档案，⼀个档案属于⼀个学⽣，那么学⽣表和档案表就是⼀对⼀关
  #系。学⽣表是主表，档案表是从表，从表中有⼀个外键和学⽣表关联，并且要求外
  #键取值唯⼀。对应关键字为：OneToOneField
  #创建模型
  class Student(models.Model):
   sno = models.CharField(max_length=6,primary_key=True)
   sname = models.CharField(max_length=100,null=False)
   ssex = models.CharField(max_length=2,default='男',null=True)
   sage = models.IntegerField(null=True)
   sclass = models.CharField(max_length=10,null=True)
   def __str__(self):
   return "no:{},name:{}".format(self.sno,self.sname)
   class Meta:
   db_table = 'student'
  class Archives(models.Model):
   idcard = models.CharField(max_length=18, unique=True)
   address = models.CharField(max_length=200,null=True)
   # on_delete=models.CASCADE 级联删除，删除学⽣会连同档案⼀块删除
   student = models.OneToOneField(Student, on_delete=models.CASCADE)
   def __str__(self):
   return "{},{}".format(self.idcard,self.address)
   class Meta:
   db_table = 'archives'

• 增加数据

  ---

  def addstudent(request):
   student = Student()
   student.sno = '180502'
   student.sname = '杨康'
   student.sage = 22
   student.save()
   return HttpResponse("增加了⼀个学⽣")
  def addarchives(request):
   stu = Student.objects.get(pk='180503')
   arc = Archives()
   arc.idcard = '130098384893838953'
   arc.student = stu #学⽣对象必须已经保存到数据库，否则错误
   arc.save()
   return HttpResponse("增加档案")

• 删除数据

  ---

  def deletestudent(request):
   student = Student.objects.get(pk='180503')
   student.delete()
   return HttpResponse("删除")

• 正反向查询

  ---

  # 正向查询
  def findstudent(request):
   # 获取学⽣信息
   student = Student.objects.first()
   print(student)
   # 通过学⽣对象获取档案信息
   archive = student.archives
   print(archive)
   return HttpResponse(student)
  
  
  #反向查询
  def findarchives(request):
   #获取档案记录
   archive = Archives.objects.first()
   #通过档案获取关联学⽣信息
   student = archive.student
   return HttpResponse(student)

• 跨关系查询

  ---

  def lookup(request):
   #根据档案查学⽣
   # student = Student.objects.get(archives__pk=1)
   student =
  Student.objects.get(archives__idcard='13009488384383838')
   #根据学⽣查档案
   archive = Archives.objects.get(student__sno='180501')
   return HttpResponse(archive)

• 级联删除

  ---

  on_delete
  CASECADE 默认，默认级联删除数据
  PROTECT 保护模式，当从表中存在级联记录的时候，删除主表记录会抛
  出保护异常，从表中不存在级联数据的时候，是允许删除的
  SET_XXX
  NULL 外键字段本身必须允许为空
  DEFAULT 外键字段本身有默认值
  DO_NOTHING 什么都不做