等效的 linq 查询语法

Question

GroupBy 的以下重载的等效查询语法是什么：

public static IEnumerable<IGrouping<TKey, TElement>> 
   GroupBy<TSource, TKey, TElement>(
      this IEnumerable<TSource> source,
      Func<TSource, TKey> keySelector,
      Func<TSource, TElement> elementSelector
)

在尝试编写以下等效查询语法时出现了这个问题：

var groups = 
    products.SelectMany(p => p.Categories,
                    (p, c) => new { Product = p, Category = c })
            .GroupBy(p => p.Category, p => p.Product);

“正常”查询语法会返回冗余信息：Category 已由 Key 属性给出：

var groups = from p in products
             from c in p.Categories
             let pc = new { Product = p, Category = c }
             group pc by pc.Category into g
             select g;

相当于：

var groups = 
    products.SelectMany(p => p.Categories,
                    (p, c) => new { Product = p, Category = c })
            .GroupBy(p => p.Category);

回复this question时出现此问题。

Answer 1

group 和 by 之间的表达式是元素选择器。您特意添加您不想要的信息到该元素中。你只需要……不要那样做。

var groups = from product in products
             from category in product.Categories
             group product by category into g
             select g;