Django支付系统中的并发更新：如何使用F()表达式避免投票数双倍增加

# 假设 profile_obj 已经获取
profile_obj.totalVote += payment.vote
profile_obj.save()

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

# ... 其他导入 ...

@transaction.atomic
def verify_payment(request, ref):
    print(f"verify_payment called for reference: {ref}")
    try:
        payment = Payment.objects.get(ref=ref)
    except Payment.DoesNotExist:
        print("Invalid payment reference:", ref)
        return render(
            request,
            "competitions/error.html",
            {"error_message": "Invalid payment reference."},
        )

    # 关键：检查支付是否已经验证过并处理，防止重复更新
    if payment.verified:
        print(f"Payment with reference {ref} already verified and processed. Skipping vote update.")
        return render(request, "competitions/success.html")

    # 调用 Payment 模型的方法进行外部支付网关验证
    verified = payment.verify_payment()

    if verified:
        contestant = payment.contestant
        profile_obj = contestant.user.profile

        # 使用 F() 表达式进行原子更新，直接在数据库层面操作
        # 这将确保 totalVote 的更新是原子性的，避免竞态条件
        profile_obj.totalVote = F('totalVote') + payment.vote
        profile_obj.save()

        # 如果需要立即获取更新后的值用于日志或其他操作，需要从数据库重新加载
        profile_obj.refresh_from_db()

        print(f"Payment verified for with total votes of {profile_obj.totalVote}.")

        return render(request, "competitions/success.html")
    else:
        return render(
            request,
            "competitions/error.html",
            {"error_message": "Payment verification failed."},
        )