如何对Django查询的.count返回值做算术运算并传到模板

• count是Django ORM提供的统计查询方法，不是属性，必须加()调用才能返回实际的数值结果。你代码中直接写.count拿到的是方法对象本身，无法进行算术运算，这是代码运行报错的直接原因。

def get_context_data(self, **kwargs):
    context = super(Index, self).get_context_data(**kwargs)

    # 给count加括号调用，拿到统计数值
    amount_one = mymodel.objects.filter(status='status1').count()
    amount_two = mymodel.objects.filter(status='status2').count()

    total_amount = amount_one + amount_two
    # 增加除零防护，避免没有匹配数据时抛出异常
    if total_amount == 0:
        result_amount = 0
    else:
        result_amount = (amount_one * 100) // total_amount

    context['result'] = result_amount

    return context

上述代码会发起2次数据库查询，数据量较大时可以用aggregate一次查询拿到所有统计结果，减少数据库IO开销：

from django.db.models import Count, Q

def get_context_data(self, **kwargs):
    context = super(Index, self).get_context_data(**kwargs)

    # 一次查询同时统计两个状态的数量
    count_data = mymodel.objects.aggregate(
        amount_one=Count('pk', filter=Q(status='status1')),
        amount_two=Count('pk', filter=Q(status='status2'))
    )
    amount_one = count_data['amount_one']
    amount_two = count_data['amount_two']

    total_amount = amount_one + amount_two
    result_amount = (amount_one * 100) // total_amount if total_amount !=0 else 0

    context['result'] = result_amount

    return context

你在模板中可以直接调用{{ result }}展示最终的百分比数值。

内容的提问来源于stack exchange，提问作者Risker