Python 在admin-Django中使用sum和display数据进行多注释

我对Django和Python都是新手。目前，我正在尝试Django管理员

我有三种Django应用程序模型，分别是

GoodsItem

、

SoldGoodsItem

和

FinishedGoodsItem

。models.py是：

from django.db import models


class GoodsItem(models.Model):
    name = models.CharField(max_length=255)
    size = models.DecimalField(max_digits=4, decimal_places=2)
    INCHES = 'IN'
    NUMBER = 'NUM'
    GOODS_ITEM_SIZE_UNITS = (
        (INCHES, 'Inches'),
        (NUMBER, '#'),
    )
    size_unit = models.CharField(
        max_length=4,
        choices=GOODS_ITEM_SIZE_UNITS,
        default=INCHES,
    )

    def __str__(self):
        if(self.size_unit == self.NUMBER):
            return "%s #%s" % (self.name, (self.size).normalize())
        else:
            return "%s %s\"" % (self.name, (self.size).normalize())


class FinishedGoodsItem(models.Model):
    date = models.DateField()
    goods_item = models.ForeignKey(GoodsItem, on_delete=models.CASCADE, related_name="finished_name")
    weight = models.DecimalField(max_digits=6, decimal_places=3)

    def __str__(self):
        return str(self.goods_item)


class SoldGoodsItem(models.Model):
    goods_item = models.ForeignKey(GoodsItem, on_delete=models.CASCADE, related_name="sold_name")
    date = models.DateField()
    weight = models.DecimalField(max_digits=6, decimal_places=3)

    def __str__(self):
        return str(self.goods_item)

这里是admin.py：

from django.contrib import admin
from django.db.models import Sum

from .models import GoodsItem, FinishedGoodsItem, SoldGoodsItem

@admin.register(SoldGoodsItem)
@admin.register(FinishedGoodsItem)
class FinishedGoodsItemAdmin(admin.ModelAdmin):
    fields = ('date', 'goods_item', 'weight')
    list_display = ('date', 'goods_item', 'weight')

@admin.register(GoodsItem)
class GoodsItemAdmin(admin.ModelAdmin):
    list_display = ('__str__', 'finished_good', 'sold_good', 'stock_available')

    def get_queryset(self, request):
        qs = super(GoodsItemAdmin, self).get_queryset(request)
        qs = qs.annotate(
            finished_good=Sum('finished_name__weight'),
            sold_good=Sum('sold_name__weight'),
            stock_available=Sum('finished_name__weight') - Sum('sold_name__weight'),
        )
        return qs

    def finished_good(self, obj):
        return obj.finished_good

    def sold_good(self, obj):
        return obj.sold_good

    def stock_available(self, obj):
        return obj.stock_available

---

在每个

GoodsItem

的

stock\u available

中，我想显示

FinishedGoodsItem

的所有条目与

SoldGoodsItem

的所有条目之间的差异。目前，我得到的所有三个带注释字段的值都不正确，它们是

已完成商品

，

已售出商品

和

库存可用

。我找不到原因。在Django调试工具栏中，提示正在执行重复的查询。

这是一个已知问题，当我们尝试组合多个聚合时会发生，如中所述

作为这个特殊问题的解决方法，我们可以使用子查询表达式。这是我在

GoodsItemAdmin

的

get\u queryset

方法中使用子查询表达式更新的admin.py

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

from .models import GoodsItem, FinishedGoodsItem, SoldGoodsItem

@admin.register(SoldGoodsItem)
class SoldGoodsItemAdmin(admin.ModelAdmin):
    fields = ('date', 'goods_item', 'weight')
    list_display = ('date', 'goods_item', 'weight')

@admin.register(FinishedGoodsItem)
class FinishedGoodsItemAdmin(admin.ModelAdmin):
    fields = ('date', 'goods_item', 'weight')
    list_display = ('date', 'goods_item', 'weight')

@admin.register(GoodsItem)
class GoodsItemAdmin(admin.ModelAdmin):
    list_display = ('__str__', 'finished_good', 'sold_good', 'stock_available')

    def get_queryset(self, request):
        qs = super(GoodsItemAdmin, self).get_queryset(request)
        qs = qs.annotate(
            finished_good = Subquery(FinishedGoodsItem.objects.filter(goods_item=OuterRef('pk'))\
                .values('goods_item_id').annotate(sum=Sum('weight')).values('sum')[:1]),
            sold_good = Subquery(SoldGoodsItem.objects.filter(goods_item=OuterRef('pk'))\
                .values('goods_item_id').annotate(sum=Sum('weight')).values('sum')[:1])
        )
        return qs

    def finished_good(self, obj):
        return obj.finished_good

    def sold_good(self, obj):
        return obj.sold_good

    def stock_available(self, obj):
        finished_good = 0 if self.finished_good(obj) is None else self.finished_good(obj)
        sold_good = 0 if self.sold_good(obj) is None else self.sold_good(obj)
        return '-' if (finished_good == 0 and sold_good == 0) else finished_good - sold_good

---

希望有人觉得这很有用。

我发现这很有用，下面是使用此方法简单计算的方法（具体地说，计算与每个ThisTable行相关的相关行的相关行数）：

count=Subquery（models.ThisTable.objects.filter（id=OuterRef（'id'））.annotate（count=count（'related\u outerrelated'））.values（'count'）

这对我不起作用，子查询只返回一个权重，不做任何求和。