Question

简单的一行：

var x = (from a in arr select a).First();
Console.WriteLine(“First" + x);

如何转换为Lambda表达式？

Answer 1

所以你想将LINQ查询从使用查询语法转换为普通扩展方法调用吗？

// var first = (from a in arr select a).First();
var first = arr.First();

// var last = (from a in arr select a).Last();
var last = arr.Last();

// var filtered = (from a in arr where a == 10 select a).First();
// there are a couple of ways to write this:
var filtered1 = arr.Where(a => a == 10)
                   .First();
var filtered2 = arr.First(a => a == 10); // produces the same result but obtained differently

// now a very complex query (leaving out the type details)
// var query = from a in arr1
//             join b in arr2 on a.SomeValue equals b.AnotherValue
//             group new { a.Name, Value = a.SomeValue, b.Date }
//                 by new { a.Name, a.Group } into g
//             orderby g.Key.Name, g.Key.Group descending
//             select new { g.Key.Name, Count = g.Count() };
var query = arr1.Join(arr2,
                      a => a.SomeValue,
                      b => b.AnotherValue,
                      (a, b) => new { a, b })
                .GroupBy(x => new { x.a.Name, x.a.Group },
                         x => new { x.a.Name, Value = x.a.SomeValue, x.b.Date })
                .OrderBy(g => g.Key.Name)
                .ThenByDescending(g => g.Key.Group)
                .Select(g => new { g.Key.Name, Count = g.Count() });

Answer 2

当您使用(from y in x select y)表单时，几乎总是可以写x。

转换为LINQ lambda表达式

2 个答案: