解决Django支付后投票计数双重增加问题：F()表达式与并发控制

profile_obj.totalVote += payment.vote
profile_obj.save()

from django.db.models import F

# ...

# 错误的做法，可能导致竞态条件
# profile_obj.totalVote += payment.vote
# profile_obj.save()

# 正确的做法，使用 F() 表达式进行原子性更新
profile_obj.totalVote = F('totalVote') + payment.vote
profile_obj.save(update_fields=['totalVote']) # 优化：仅更新指定字段

from django.db import transaction
from django.db.models import F
from django.shortcuts import render, get_object_or_404
# from .models import Payment, Contestant, Profile # 假设 Profile 模型在 user.profile
# from .utils import Paystack # 假设 Paystack 支付工具类

# 导入必要的模型和设置，根据实际项目结构调整
# from django.conf import settings
# import secrets # 用于生成ref

# 假设 Payment, Contestant, Profile 模型以及 Paystack 工具类已定义
# class Payment(models.Model): ...
# class Contestant(models.Model): ...
# class Profile(models.Model): ... (假设 Contestant.user.profile 指向 Profile)

@transaction.atomic
def verify_payment(request, ref):
    print(f"DEBUG: verify_payment called for reference: {ref}")
    try:
        # 使用 select_for_update() 锁定 Payment 记录，防止并发修改其 verified 状态
        payment = Payment.objects.select_for_update().get(ref=ref)
    except Payment.DoesNotExist:
        print(f"ERROR: Invalid payment reference: {ref}")
        return render(
            request,
            "competitions/error.html",
            {"error_message": "Invalid payment reference."},
        )

    # 1. 幂等性检查：如果支付已验证，则直接返回成功，避免重复处理
    if payment.verified:
        print(f"INFO: Payment {ref} already verified. Skipping vote update.")
        return render(request, "competitions/success.html")

    # 2. 调用支付网关验证支付
    # payment.verify_payment() 方法应负责与支付网关交互，并更新 payment.verified 字段
    verified = payment.verify_payment() # 此方法内部会设置 payment.verified = True 并保存

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

        # 3. 详细日志记录：记录更新前状态
        initial_total_vote = profile_obj.totalVote
        print(f"DEBUG: Before update - Profile {profile_obj.id} (User: {contestant.user.username}) totalVote = {initial_total_vote}, adding {payment.vote} votes for payment {ref}.")

        # 4. 使用 F() 表达式进行原子性投票计数更新
        profile_obj.totalVote = F('totalVote') + payment.vote
        profile_obj.save(update_fields=['totalVote']) # 仅更新 totalVote 字段

        # 5. 从数据库刷新对象以获取最新值（如果后续代码需要）
        profile_obj.refresh_from_db()

        # 6. 详细日志记录：记录更新后状态
        print(f"INFO: After update - Profile {profile_obj.id} totalVote = {profile_obj.totalVote}. Payment {ref} successfully processed.")

        return render(request, "competitions/success.html")
    else:
        print(f"ERROR: Payment verification failed for reference: {ref}. Status not verified by gateway.")
        return render(
            request,
            "competitions/error.html",
            {"error_message": "Payment verification failed."},
        )

# 假设 Payment 模型中的 verify_payment 方法
# class Payment(models.Model):
#     # ... 其他字段 ...
#     verified = models.BooleanField(default=False)
#
#     def verify_payment(self):
#         if not self.verified:
#             paystack = Paystack() # 假设 Paystack 实例
#             status, result = paystack.verify_payment(self.ref, self.amount)
#             if status and result["amount"] / 100 == self.amount:
#                 self.verified = True
#                 self.save(update_fields=['verified']) # 只更新 verified 字段
#         return self.verified