Linq to SQL .Sum()没有组...进入

Question

我有这样的事情:

var itemsInCart = from o in db.OrderLineItems
                  where o.OrderId == currentOrder.OrderId
                  select new { o.OrderLineItemId, ..., ..., o.WishListItem.Price}

有没有办法做

itemsCart.Sum() //not sure what to pass into the function

得到o.WishListItem.Price的总和还是我必须从数据库中获取另一个iQueryable <T> with ... into？

Answer 1

关于什么:

itemsInCart.AsEnumerable().Sum(o=>o.Price);

AsEnumerable有所不同,此查询将在本地执行(Linq To Objects).

Answer 2

您可以:

itemsCart.Select(C => c.Price).SUM();

只打一次db:

var itemsInCart = (from o in db.OrderLineItems
                  where o.OrderId == currentOrder.OrderId
                  select new { o.OrderLineItemId, ..., ..., o.WishListItem.Price}
                  ).ToList();
var sum = itemsCart.Select(c=>c.Price).Sum();

额外的往返保存是值得的:)

Answer 3

尝试:

itemsCard.ToList().Select(c=>c.Price).Sum();

实际上这会表现得更好:

var itemsInCart = from o in db.OrderLineItems
              where o.OrderId == currentOrder.OrderId
              select new { o.WishListItem.Price };
var sum = itemsCard.ToList().Select(c=>c.Price).Sum();

因为您只需从数据库中检索一列.