c# - LINQ 查询以选择畅销书

Question

聪明人可以帮我写一个 LINQ 查询来获得最畅销的产品，我在实体框架模型中有这两个表/类：

Orders (OrderedItems)
OrderedItem (Product, Qty)

例如。（这显然行不通）

Orders.OrderByDescending(o => Sum(o.OrderedItems.Qty))
      .Select(o => o.OrderedItems.Product)

Answer 1

您根本不需要 Orders 表。假设每个订购的商品都有相应的订单，您应该能够做到这一点。

var query =
    (from item in OrderedItem
    group item.Qty by item.Product into g
    orderby g.Sum() descending
    select g.Key).Take(5); // get the top 5 orders

Answer 2

class Product {
            public int Id { get; set; }
        }
        class OrderedItem
        {
            public Product Product { get; set; }

            public int Qty { get; set; }
        }

进而：

        List<OrderedItem> orders = new List<OrderedItem>();
        var products = orders.GroupBy(p => p.Product.Id).OrderByDescending(pi => pi.Sum(pii => pii.Qty)).Select(p=>p.Key);

Answer 3

我认为您使用Sum不正确。我想这就是你想要的

Orders.OrderByDescending(o => o.OrderedItems.Sum(oi => oi.Qty))
      .Select(o => o.OrderedItems.Product)

Answer 4

    public IQueryable<Product> Bestsellers(int? count)
    {
        var query = (from item in db.OrderDetails
                     group item.Qty by item.Product into g
                     orderby g.Sum() descending
                     select g.Key).Take(count??20); // get the top 5 orders

        return query;
    }