Django ORM 如何舍入平均结果 [英] Django ORM how to Round an Avg result

问题描述

我有一个模型，在该模型中我使用 Django ORM 从表中提取平均值.我想四舍五入那个 Avg 值，我该怎么做?

I have a model in which I use Django ORM to extract Avg of values from the table. I want to Round that Avg value, how do I do this?

见下文，我从按日期分组的价格模型中提取平均价格，格式为 YYYY-MM，我想自动提取四舍五入到最接近数字的平均值.

See below I am extracting Avg price from Prices model grouped by date in format YYYY-MM, I want to automatically extract the average values rounded to the closest number.

rs = Prices.objects.all.extra(select={
    'for_date': 'CONCAT(CONCAT(extract( YEAR from for_date ), "-"),
        LPAD(extract(MONTH from for_date), 2, "00"))'
    }).values('for_date').annotate(price=Avg('price')).order_by('-for_date')

推荐答案

使用 Func() 表达式.

这是使用 Django 聚合主题指南 在 SQLite 中四舍五入到两位小数:

Here's an example using the Book model from Django Aggregation topic guide to round to two decimal places in SQLite:

class Round(Func):
    function = 'ROUND'
    template='%(function)s(%(expressions)s, 2)'

Book.objects.all().aggregate(Round(Avg('price')))

这允许参数化轮函数(来自@RichardZschech 的回答):

This allows the round function to be parameterised (from @RichardZschech's answer):

class Round(Func):
  function = 'ROUND'
  arity = 2

Book.objects.all().aggregate(Round(Avg('price'), 2))

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