django 按非相关表中的汇总值排序答案

【问题标题】：django order by aggregate value from non-related tabledjango 按非相关表中的汇总值排序
【发布时间】：2021-11-10 05:34:23
【问题描述】：

我有Accrual和Member三个模型，这两个模型的共同字段是register_no，但是这个字段不是外键

class Accrual(models.Model):
  register_no = models.PositiveIntegerField(verbose_name=_('Register No'))
  amount=models.DecimalField(decimal_places=2, max_digits=17, verbose_name=_('Total Amount'))

class Member(models.Model):
    register_no = models.PositiveIntegerField(unique=True, verbose_name=_('Register No'))

class Driver(models.Model):
    register_no = models.PositiveIntegerField(unique=True, verbose_name=_('Register No'))

我想列出每个成员/司机的债务。可以通过@property 来完成；

class Member(models.Model):
    register_no = models.PositiveIntegerField(unique=True, verbose_name=_('Register No'))

    @property
    def debt(self):
        ret_val = Accrual.objects.filter(register_no=self.register_no).aggregate(
            debt=Sum('amount'))

        debt = ret_val.get('debt', 0)
        return debt if debt else 0

但我不能以这种方式使用 order_by。我想按债务对每个成员进行排序。我该如何解决这个问题？

【问题讨论】：

标签： django django-models django-rest-framework django-queryset django-orm

【解决方案1】：

您可以使用子查询添加基于register_no的所有相关应计：

from django.db.models import OuterRef, Subquery, Sum


accruals = Accrual.objects.filter(
  register_no=OuterRef('register_no')
).values('register_no').annotate(debt=Sum('amount'))

Member.objects.annotate(
  debt=Subquery(accruals.values('debt'))
).order_by('debt')

产生这个 sql：

SELECT "id", "register_no", (
    SELECT SUM(U0."amount") AS "debt" 
    FROM "accrual" U0 
    WHERE U0."register_no" = ("register_no") 
    GROUP BY U0."register_no"
) AS "debt" 
FROM "member" 
ORDER BY "debt" ASC

【讨论】：