C#四层嵌套列表处理：仅添加Coupons列表非空的关联元素

现有四层嵌套列表结构，层级由外到内依次为Companies、Shops、Campaigns、Coupons，所有数据均从服务端拉取。需要实现过滤规则：仅当最内层Coupons列表非空时，才将对应的关联层级元素添加到结果列表，过滤所有Coupons为空的无效数据。

原有业务实现代码如下：

foreach (var row in Companies)
{
    reportData.companies.Add(new Companies { ID = row.Id, name = row.BrandName });

    var Shops = logicService.CompanyShopService.GetShopsByCompany(row.Id);
    var Campaigns = logicService.CampaignService.GetCampaignsByCompany(row.Id);

    foreach (var shop in Shops)
    {
        reportData.companies.Where(item => item.ID == shop.ClientID).FirstOrDefault().shops.Add(new Distribution_Shops { Id = shop.Id, Name = shop.Name });
        var shop_campaigns = Campaigns.Where(item => item.ShopID == shop.Id);
        foreach (var campaign in shop_campaigns)
        {
            var coupons = logicService.CouponsService.GetAllByCampaign(campaign.Id, false);

            foreach (var company in reportData.companies)
            {
                foreach (var tmp_shop in company.shops)
                {
                    
                    if (tmp_shop.Id == shop.Id)
                    {
                        tmp_shop.campaigns.Add(new Distribution_Campaign { Id = campaign.Id, Name = campaign.CampaignName, coupons = coupons});
                        
                    }
                }
            }
        }
    }
}

• 先添加Company、Shop节点后再补Campaign数据，会残留大量Coupons为空的无效Shop、Company节点，达不到过滤要求
• 存在多层冗余全量遍历：每次添加Campaign时都循环所有已加入的Company和Shop，数据量较大时性能损耗明显
• 未做Coupons非空判断，空Coupons对应的Campaign、关联的Shop和Company都会被错误加入结果集
• 缺少空值校验，FirstOrDefault()可能返回null值，直接调用shops.Add会触发空引用运行时错误

核心逻辑为从最内层数据开始校验，只有内层存在有效非空数据时，才构造外层对应节点加入结果，从根源避免无效数据进入结果集，无需后续二次过滤。

foreach (var companyRow in Companies)
{
    // 预拉取当前公司下关联的所有门店、活动数据
    var shops = logicService.CompanyShopService.GetShopsByCompany(companyRow.Id);
    var allCompanyCampaigns = logicService.CampaignService.GetCampaignsByCompany(companyRow.Id);
    
    var validCompany = new Companies { ID = companyRow.Id, name = companyRow.BrandName };
    bool companyHasValidData = false;

    foreach (var shop in shops)
    {
        var validShop = new Distribution_Shops { Id = shop.Id, Name = shop.Name };
        bool shopHasValidCampaign = false;
        
        // 筛选当前门店绑定的所有活动
        var shopCampaigns = allCompanyCampaigns.Where(c => c.ShopID == shop.Id);
        foreach (var campaign in shopCampaigns)
        {
            // 拉取活动下的优惠券，仅非空时保留该活动
            var coupons = logicService.CouponsService.GetAllByCampaign(campaign.Id, false);
            if (coupons != null && coupons.Any())
            {
                validShop.campaigns.Add(new Distribution_Campaign 
                { 
                    Id = campaign.Id, 
                    Name = campaign.CampaignName, 
                    coupons = coupons 
                });
                shopHasValidCampaign = true;
            }
        }

        // 门店下存在带有效优惠券的活动时，才将门店加入公司节点
        if (shopHasValidCampaign)
        {
            validCompany.shops.Add(validShop);
            companyHasValidData = true;
        }
    }

    // 公司下存在有效门店数据时，才将公司加入最终结果集
    if (companyHasValidData)
    {
        reportData.companies.Add(validCompany);
    }
}

• 过滤逻辑从最内层Coupons触发，只有Coupons非空才会逐层向上添加关联的Campaign、Shop、Company节点，完全过滤无效链路数据
• 移除了原有代码中多层嵌套的冗余遍历，构造节点时直接挂载到对应父级，执行效率更高
• 增加了空值判断，避免空引用异常
• 通过布尔标记位记录每层有效数据状态，不需要对结果集做二次遍历清理

内容的提问来源于stack exchange，提问作者Arthur