Django框架models使用group by详解

Z时代
2024-01-10
分类：综合

Django框架models使用group by详解：

首先，看下列代码：

UserData.objects.filter(hubid=sensorid,time__range=(time2,time1)).values('hour').annotate(sum_out=Sum('outdoor'), sum_in=Sum('indoor'), sum_eat=Sum('kitchen'), sum_wash=Sum('toilet')).order_by('hour')

上述代码相当于sql语句：

select Sum('outdoor') as sum_out,Sum('indoor') as sum_in,Sum('kitchen') as sum_eat,Sum('toilet') as sum_wash,hour
where hubid='sensorid' and (time between time1 and time2)
group by hour
order by hour asc

另外，在Django中order_by(‘hour')表示按生序排列，若要按降序排列，则使用order_by(‘-hour')

补充知识：django模型orm进行group by

场景：三个模型分别为教师，学生，课程。一个教师可主讲多门课程，但一门课程只能由一个教师主讲，即教师和课程是一对多的关系。一个学生可选多门课程，一门课程可被多个学生选，即学生和教师为多对多的关系。


class Teacher(models.Model):
  name = models.CharField(max_length=20, verbose_name='教师姓名')
  def __unicode__(self):
    return self.name
class Student(models.Model):
  name = models.CharField(max_length=20, verbose_name='学生姓名')
  def __unicode__(self):
    return self.name
class Course(models.Model):
  name = models.CharField(max_length=20, verbose_name='课程名')
  teacher = models.ForeignKey(Teacher, verbose_name='主讲人')
  student = models.ManyToManyField(Student, verbose_name='选课学生')
  def __unicode__(self):
    return self.name

选取某教师主讲的pk最小的课：