Linq to SQL-按问题排序 [英] Linq to SQL - Order by issue

问题描述

另一个分配块！

基本上，问题是我无法让输出按降序对价格进行排序，而又无法将其按国家/地区分组.

Basically the problem is that I can't get my output to order the price in a descending order while keeping it grouped by Country.

我知道这可能很简单，但我似乎无法理解.

I know it's probably something so simple but I just can't seem to get it.

有解决方案吗?

谢谢！

这里是一个问题: "6.允许用户按国家/地区降序查看排名前五位的畅销产品. (10分)"

Here is the question: "6. Allow the user view the top five selling products in descending order grouped by country. (10 marks)"

这是我的代码:

void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
        var q6 = (from t in northwind.Products
                 orderby t.UnitPrice descending
                 join o in northwind.Suppliers on t.SupplierID equals o.SupplierID
                 group t.UnitPrice by new {o.Country, t.UnitPrice} into grouped
                 select new
                 {
                     Output = grouped.Key

                 }).Take(5);                

        lbxTop5.ItemsSource = q6;
    }

推荐答案

"6.允许用户按国家/地区降序查看排名前五位的畅销产品.(10分)"

"6. Allow the user view the top five selling products in descending order grouped by country. (10 marks)"

我可以用两种方式阅读.

I could read that two ways.

A)获取最畅销的五种产品，按国家对这五种产品进行分组. 或者 B)对于每个国家/地区，最畅销的五个产品是什么?

A) Get the top five selling products, group those 5 products by country. OR B) For each country, what are the top five selling products?

我认为B更有意义，所以我会做到这一点.

I think B makes more sense, so I'll do that one.

另外-什么是最畅销的产品?这个国家和它有什么关系?我认为客户所在国家/地区比供应商所在国家/地区更为重要.另外-我认为OrderDetails中的数量可以告诉我哪些产品最畅销.注意:您的讲师可能会提出除我以外的其他想法，因此使用这些假设后果自负.

Also - what is a top selling product? and how is the country related to it? I think that the Customer's country matters more than the Supplier's. Also - I think that Quantity in the OrderDetails can tell me which products are top selling. Note: your instructor may have other ideas than I do, so use these assumptions at your own peril.

from c in northwind.Customers
from o in c.Orders  //all froms except first are calls to SelectMany (one to many)
from od in o.OrderDetails //navigational properties -> no need to write explicit joins
let p = od.Product  // now we go many to one, so we don't need SelectMany
group od
  by new {c.Country, Product = p }   //anon grouping key
  into productGroup
let country = productGroup.Key.Country
let product = productGroup.Key.Product
let quantity = productGroup.Sum(od2 => od2.Quantity)
group new {Product = product, Quantity = quantity} //anon group elements
  by country
  into countryGroup
select new {
  Country = countryGroup.Key,
  Summaries = countryGroup
    .OrderByDescending(summary => summary.Quantity)
    .ThenBy(summary => summary.Product.ProductId) //tiebreaker
    .Take(5)
    .ToList()
}

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