F,Q,aggregate

Posted 2020-12-16 liuxiaomo

# models


class Student(models.Model):
    name = models.CharField(max_length=32)
    age = models.IntegerField()
    def __str__(self):
        return self.name

# views
# aggregate
from django.db.models import F, Q, Count, Avg, Max, Min, Sum
def agg_orm(request):
    if request.method == ‘GET‘:
        stu = models.Student.objects.aggregate(
            stu_num = Count(‘age‘),
            stu_avg = Avg(‘age‘),
            stu_max = Max(‘age‘),
            stu_min = Min(‘age‘),
            stu_sum = Sum(‘age‘)
        )
        print(stu)
        # 运行结果 ：{‘stu_num‘: 24, ‘stu_avg‘: 28.6667, ‘stu_max‘: 41, ‘stu_min‘: 22, ‘stu_sum‘: 688}
    return HttpResponse(‘ok‘)

#F Q

def stu_orm(request):
    if request.method == ‘GET‘:
        #  F 表达式表示数据库表的某一列至
        #  F 表达式可以在不实际把数据存入python内存的前提下，引用值和操作数据库
        # print(models.Student.objects.all().update(age=F("age") + 1))


        # Q 复杂查询，多应用查找
        # 可以组合 &（and） |(or) ~(not) 操作 当操作字符用于俩个Q的对象产生一个新的Q对象
        # 例如：Q(Q(pk=8) | Q(pk__gt=10)) & Q(name=‘root‘)
        stus = models.Student.objects.filter(
            Q(age__gt=1) & Q(age__lt=30),
            Q(name__startswith=‘tom‘)
        )
        print(‘stu‘, stus)

        # stu_list = [
        #     {"name":‘tom‘,‘age‘:11},
        #     {"name":"nike",‘age‘:12},
        #     {‘name‘:‘xiaomo‘,‘age‘:30}
        # ]
        #
        # for stu in stu_list:
        #     models.Student.objects.create(**stu)
    return HttpResponse(‘ok‘)