如何对 Django 模型的一对多相关字段执行条件聚合？

Question

给定以下模型架构：

class Transaction(models.Model):
  wallet = models.ForeignKey(related_name="transactions")
  amount = models.DecimalField()  # must be positive value
  type = models.CharField(choices=[("deposit", "deposit"), ("withdrawal", "withdrawal")]

class Wallet(models.Model):
  pass

获取数据库中每条钱包记录余额的最有效的 Django ORM 查询是什么？

current_balance = sum of "amounts", where type="deposits" - sum of "amounts", where type="withdrawal"

假设我们无法更改给定表/记录的列或字段，并且 amount 必须保持正值。

想法？

Answer 1

也许我们可以合作：

from django.db.models import Sum

Wallet.objects.annotate(
    balance=Sum('transactions__amount', <strong>filter=Q(transactions__type='deposit')</strong>) -
            Sum('transactions__amount', <strong>filter=Q(transactions__type='withdrawal')</strong>)
)

但我建议在提款的情况下将金额设为负数，在这种情况下我们可以简单地总结交易：

# when using negative amounts for withdrawals

from django.db.models import Sum

Wallet.objects.annotate(
    balance=Sum('transactions__amount')
)

如何对 Django 模型的一对多相关字段执行条件聚合？

How to perform conditional aggregation on a Django model's one to many related field?

django

orm

django-orm

django-aggregation