Django库存同步异常：编辑供应商产品时库存未自动增减

目前供应商产品自身数量可正常更新，但编辑供应商产品数据时，数据库中的Stocks表库存既不增加也不减少。需求为：编辑产品时，若新数量大于旧数量，库存增加新旧数量的差值；若新数量小于旧数量，库存减少该差值。

相关代码 #

models.py

# models.py
from collections.abc import Collection
from django.contrib.auth.models import User
from django.db import models
from django.core.exceptions import ValidationError

class Client(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    mobile = models.CharField(max_length=15)
    address = models.CharField(max_length=255)

    def clean_mobile(self):
        mobile=self.mobile
        if len(str(mobile))!= 10:
            raise ValidationError("invalid mobile number")
        return mobile


class Supplier(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    product_name = models.CharField(max_length=255)
    product_price = models.DecimalField(max_digits=10, 
    decimal_places=2)
    image = models.ImageField(upload_to='products/')
    quantity= models.PositiveIntegerField(default=1)
    category=models.CharField(choices=CHOICES3,max_length=10)
        
    def __str__(self):
        return self.product_name

CHOICES3 = [('Tshirt','Tshirt'),('Jeans','Jeans'),('Jacket','Jacket'),('Shoes','Shoes'),('Watch','Watch')]
CHOICES2 = [('Polo-Tshirt','Polo-Tshirt'),('Levis-Jeans','Levis-Jeans'),('Denim-Jacket','Denim-Jacket'),('Puma-Shoes','Puma-Shoes'),('Titan-Watch','Titan-Watch')]


class Stocks(models.Model):
    product_name = models.CharField(choices=CHOICES2,max_length=100)
    quantity = models.PositiveBigIntegerField(default=100)


    def __str__(self):
         return self.product_name

views.py

def supplier_dashboard(request):
    if request.method == 'POST':
        product_name = request.POST.get('product_name')
        product_price = request.POST.get('product_price')
        image = request.FILES.get('image')
        quantity = request.POST.get('quantity')
        category = request.POST.get('category')
        data = Supplier.objects.create(user=request.user, category=category, product_name=product_name, product_price=product_price, image=image, quantity=quantity)
        data.save()
        supplier = Supplier.objects.filter(user=request.user)
        return HttpResponseRedirect(reverse('update_stocks', args=[data.id]))
    else:
        supplier = Supplier.objects.filter(user=request.user)
    return render(request, 'enroll/supplier_dashboard.html', {'suppliers': supplier})

supplier_edit 视图

def supplier_edit(request,id):
    try:
        product=Supplier.objects.get(id=id)
        if product.user == request.user:
            if request.method=='POST':
                    product.product_name = request.POST.get('product_name')
                    product.product_price = request.POST.get('product_price')
                    if 'image' in request.FILES:
                        product.image=request.FILES.get('image')
                    product.quantity = request.POST.get('quantity')
                    product.category = request.POST.get('category')
                    product.save()
                    messages.success(request,"ProDuct Updated Succesfully")
                    return redirect('supplier_dashboard')
            return render(request,'enroll/supplier_edit.html',{'products':product})
    except Exception as e :
        messages.error(request," Some Error Occured ",e)     
        return render(request,'enroll/supplier_edit.html',{'products':product})

def update_stocks(request, id):
    print("------------", id)
    product = Supplier.objects.get(id=id)
    stocks = Stocks.objects.get(product_name=product.product_name)
    print(product.quantity, stocks.quantity)
    stocks.quantity = stocks.quantity - product.quantity
    stocks.save()
    return HttpResponseRedirect(reverse('supplier_dashboard'))

原代码仅更新了Supplier表的产品数量，未同步处理Stocks表的库存变更。需在编辑流程中对比新旧数量差值，同步调整对应库存。

修改后的supplier_edit视图代码如下：

def supplier_edit(request, id):
    try:
        product = Supplier.objects.get(id=id)
        if product.user != request.user:
            messages.error(request, "无权限编辑该产品")
            return redirect('supplier_dashboard')
        
        if request.method == 'POST':
            # 保存更新前的旧数量
            old_quantity = product.quantity
            # 获取新数量并转换为整数（避免字符串运算错误）
            new_quantity = int(request.POST.get('quantity'))
            
            # 更新产品基本信息
            product.product_name = request.POST.get('product_name')
            product.product_price = request.POST.get('product_price')
            if 'image' in request.FILES:
                product.image = request.FILES.get('image')
            product.quantity = new_quantity
            product.category = request.POST.get('category')
            product.save()
            
            # 计算数量差值，同步更新库存
            quantity_diff = new_quantity - old_quantity
            try:
                stocks = Stocks.objects.get(product_name=product.product_name)
                stocks.quantity += quantity_diff
                stocks.save()
                messages.success(request, "产品及库存更新成功")
            except Stocks.DoesNotExist:
                messages.error(request, f"未找到产品「{product.product_name}」的库存记录")
            
            return redirect('supplier_dashboard')
        return render(request, 'enroll/supplier_edit.html', {'products': product})
    except ValueError:
        messages.error(request, "数量输入无效，请输入正整数")
        return render(request, 'enroll/supplier_edit.html', {'products': product})
    except Exception as e:
        messages.error(request, f"更新失败：{str(e)}")
        return render(request, 'enroll/supplier_edit.html', {'products': product})

关键修改点 #

1. 对比新旧数量：更新产品前获取旧数量，计算与新数量的差值
2. 同步库存调整：根据差值直接更新Stocks表库存（正差值增加库存，负差值减少库存）
3. 类型转换处理：将POST获取的数量字符串转为整数，避免运算错误
4. 异常增强处理：新增Stocks记录不存在、数量输入非整数的异常提示
5. 权限逻辑优化：提前判断用户权限，减少冗余代码

内容的提问来源于stack exchange，提问作者Shivang Kant