如何在Django中用单表单修改多模型字段并实现出库扣减库存

一、创建Issue时自动扣减关联Product的库存 #

首先修正原模型中Product和Customer类的__str__方法缩进错误（原代码中该方法在类外部，无法生效），然后重写Issue类的save方法，结合事务实现库存原子性扣减：

from django.db import models
from django.db import transaction

class Product(models.Model):
    name = models.CharField(max_length=50)
    quantity = models.FloatField(default=0)

    def __str__(self):
        return self.name

class Customer(models.Model):
    name = models.CharField(max_length=100)
    primary_contact = models.CharField(max_length=10)
    secondary_contact = models.CharField(max_length=10)
    address = models.TextField(blank=True)

    def __str__(self):
        return self.name

class Issue(models.Model):
    date = models.DateTimeField(auto_now_add=True)
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    quantity = models.PositiveIntegerField()
    kt = models.IntegerField()
    rate = models.FloatField()
    vat = models.IntegerField(default=15)

    @property
    def kt_21(self):
        return self.kt / 21 * self.quantity
    
    @property
    def vat_amt(self):
        return self.quantity * self.rate * self.vat/100

    @property
    def total_amt(self):
        return self.quantity * self.rate + self.vat_amt

    def __str__(self):
        return f"{self.customer} - {self.total_amt} SAR"
    
    def save(self, *args, **kwargs):
        # 事务确保库存扣减与Issue创建原子性执行
        with transaction.atomic():
            # 校验库存是否充足
            if self.product.quantity < self.quantity:
                raise ValueError(f"产品「{self.product.name}」库存不足，当前库存: {self.product.quantity}")
            # 扣减产品库存
            self.product.quantity -= self.quantity
            self.product.save()
            # 保存Issue记录
            super().save(*args, **kwargs)

二、通过单个表单完成不同模型字段的修改 #

可以自定义表单整合多模型字段，在表单的clean方法中做数据校验，save方法中分别处理不同模型的保存逻辑：

1. 自定义表单 #

from django import forms
from .models import Issue, Product, Customer

class IssueMultiModelForm(forms.Form):
    # Issue模型字段
    customer = forms.ModelChoiceField(queryset=Customer.objects.all())
    product = forms.ModelChoiceField(queryset=Product.objects.all())
    quantity = forms.IntegerField(min_value=1)
    kt = forms.IntegerField()
    rate = forms.FloatField()
    vat = forms.IntegerField(initial=15)
    # Product模型可修改字段（示例：修改产品名称）
    product_name = forms.CharField(max_length=50, required=False, label="修改产品名称（可选）")

    def clean(self):
        cleaned_data = super().clean()
        product = cleaned_data.get("product")
        quantity = cleaned_data.get("quantity")
        
        # 提前校验库存
        if product and quantity and product.quantity < quantity:
            self.add_error("quantity", f"产品「{product.name}」库存不足")
        return cleaned_data

    def save(self):
        with transaction.atomic():
            cleaned_data = self.cleaned_data
            product = cleaned_data["product"]
            
            # 修改Product字段（若用户输入了新名称）
            if cleaned_data.get("product_name"):
                product.name = cleaned_data["product_name"]
                product.save()
            
            # 创建Issue并自动扣减库存（依赖Issue重写的save方法）
            issue = Issue.objects.create(
                customer=cleaned_data["customer"],
                product=product,
                quantity=cleaned_data["quantity"],
                kt=cleaned_data["kt"],
                rate=cleaned_data["rate"],
                vat=cleaned_data["vat"]
            )
            return issue

2. 视图中使用表单 #

from django.shortcuts import render, redirect
from .forms import IssueMultiModelForm

def create_issue_with_edit(request):
    if request.method == "POST":
        form = IssueMultiModelForm(request.POST)
        if form.is_valid():
            form.save()
            return redirect("issue_list")  # 替换为你的Issue列表页面URL
    else:
        form = IssueMultiModelForm()
    return render(request, "create_issue.html", {"form": form})

内容的提问来源于stack exchange，提问作者pip install logic