将项添加到集合中的集合

Question

这是我的对象结构，

Group has         
     List of Offers
Offer has 
     GroupId
     List of Products

如何根据组ID

将产品添加到现有产品列表中

此代码正在添加产品，但会覆盖现有产品

Group.OffersList.Where(x => x.GroupId == "1")
                .SelectMany(x => x.ProductList)
                .ToList().Add(Product);

Answer 1

Group.OffersList.Where(x => x.GroupId == "1")
                 .ToList()
                 .ForEach(x => x.Add(Product));