Python Django：我如何从另一个数字中减go 数字并在 django 中返回新值

我有一个名为main_all_earning的模型字段，看起来像这个main_all_earning = models.IntegerField(default=0)，我还有一个表单，允许用户输入他们想从main_all_earning中提取的任何金额，我已经为它编写了逻辑，从main_all_earning中减go 名为amount的表单中的值，但主的所有收入不更新.可能是什么问题？

Views.py:

def withdrawal_request(request):
    user = request.user
    profile = Profile.objects.get(user=user)
    main_all_earning = profile.main_all_earning
    
    if request.method == "POST":
        form = WithWithdrawalRequestForm(request.POST)
        
        if form.is_valid():
            new_form = form.save(commit=False)
            new_form.user = request.user

            if new_form.amount > main_all_earning:
                messages.warning(request, "You cannot withdraw more than your wallet balance.")
                return redirect("core:withdrawal-request")

            elif pending_payout >= main_all_earning:
                messages.warning(request, "You have reached your wallet limit")
                return redirect("core:withdrawal-request")
            
            elif new_form.amount >= main_all_earning:
                messages.warning(request, "You have reached your wallet limit")
                return redirect("core:withdrawal-request")

            else:
                new_form.save()
                main_all_earning = main_all_earning - new_form.amount
                messages.success(request, f"Withdrawal Request Is Been Processed... You would get a bank alert soon")
                return redirect("core:withdrawal-request")

    else:
        form = WithWithdrawalRequestForm(request.POST)
        context = {
            "form":form,
            "main_all_earning":main_all_earning,
            
        }
        return render(request, "core/withdrawal-request.html", context)

    context = {
            "form":form,
            "main_all_earning":main_all_earning,
            
        }
    return render(request, "core/withdrawal-request.html", context)