python - 在管理中用总和显示数据进行多重注释 - Django

Question

我是 Django 和 Python 的新手。目前我正在尝试使用 Django Admin。

我有一个 Django 应用程序的三个模型，它们是 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_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，我得到的所有三个注释字段的值都不正确，它们是 finished_good、sold_good 和 stock_available。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。

Answer 1

这是已知问题，当我们尝试组合多个聚合时会发生，如 docs 中所述.

作为这个特定问题的解决方法，我们可以使用子查询表达式。这是我在 GoodsItemAdmin 的 get_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

希望有人觉得这有用。