将此LINQ表达式转换为Lambda

Question

伙计们，我很难将下面的linq表达式（左连接实现）转换为lambda表达式（用于学习）。

var result = from g in grocery 
     join f in fruit on g.fruitId equals f.fruitId into tempFruit 
     join v in veggie on g.vegid equals v.vegid into tempVegg 
     from joinedFruit in tempFruit.DefaultIfEmpty() 
     from joinedVegg in tempVegg.DefaultIfEmpty() 
     select new { g.fruitId, g.vegid, fname = ((joinedFruit == null) ? string.Empty :  joinedFruit.fname), vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname) }; 

有人可以告诉我该怎么做。

，我真的很感激，如果有人给我“C＃lambda表达式& Linqs”的优秀教程链接

Answer 1

你可以看看101 LINQ Samples和C# 3.0 QUERY EXPRESSION TRANSLATION CHEAT SHEET

Answer 2

下载LINQPad;它内置了用于学习LINQ的示例。

Answer 3

使用反射.NET :)

Answer 4

下面是我按照启发式：

青睐LINQ表达了lambda表达式时，你有加入。

我认为带连接的lambdas看起来很杂乱，难以阅读。

Answer 5

我通常使用ReSharper来帮助我将事情转换为方法链和lambda，这可以帮助我来回相当容易。

var result = from g in grocery 
       join f in fruit on g.fruitId equals f.fruitId into tempFruit 
       join v in veggie on g.vegid equals v.vegid into tempVegg 
       from joinedFruit in tempFruit.DefaultIfEmpty() 
       from joinedVegg in tempVegg.DefaultIfEmpty() 
       select new { g.fruitId, g.vegid, fname = ((joinedFruit == null) ? string.Empty : joinedFruit.fname), vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname) }; 

，然后使用转换的LINQ to方法链的ReSharper的选项等于以下：

 var result =grocery .GroupJoin(fruit, g => g.fruitId, f => f.fruitId, (g, tempFruit) => new {g, tempFruit}) 
          .GroupJoin(veggie, @t => @t.g.vegid, v => v.vegid, (@t, tempVegg) => new {@t, tempVegg}) 
          .SelectMany(@t => @t.@t.tempFruit.DefaultIfEmpty(), (@t, joinedFruit) => new {@t, joinedFruit}) 
          .SelectMany(@t => @t.@t.tempVegg.DefaultIfEmpty(),(@t, joinedVegg) => 
           new 
            { 
             @t.@t.@t.g.fruitId, 
             @t.@t.@t.g.vegid, 
             fname = ((@t.joinedFruit == null) ? string.Empty : @t.joinedFruit.fname), 
             vname = ((joinedVegg == null) ? string.Empty : joinedVegg.vname) 
            }); 

授予输出小于可取的，但它在理解语法的地方开始至少帮助。

Answer 6

要转换LINQ查询到它的lambda相当于：

1. 下载Linqpad和运行 查询。
2. 在结果窗口中，单击工具栏中的“λ”按钮上的 。 正上方的结果窗口中
3. 您的查询将被转换为 Lambda表达式相当于！

Answer 7

这里是你会如何写这个查询的Lambda：

var cus­tomers = new List { 
new Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1” }, 
new Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2” }, 
}; 

var user­Cus­tomers = new List { 
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1”, User = “not-admin” }, 
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer1”, User = “admin” }, 
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer2”, User = “not-admin” }, 
new User­Cus­tomer { Com­pa­nyId = “AC”, Cus­tomerId = “Customer2”, User = “admin” }, 
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer1”, User = “not-admin”  }, 
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer1”, User = “admin” }, 
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2”, User = “not-admin” }, 
new User­Cus­tomer { Com­pa­nyId = “not-AC”, Cus­tomerId = “Customer2”, User = “admin” } 
}; 

使用查询表达式

var query = 
from c in cus­tomers 
join uc in user­Cus­tomers on 
new { c.CompanyId, c.CustomerId } equals new { uc.CompanyId, uc.CustomerId } 
where c.CompanyId == “AC” && uc.User == “admin“ 
select c; 

使用Lambda表达式

var lambda = cus­tomers.Where(c => c.CompanyId == “AC”) // inner sequence 
.Join(userCustomers.Where(uc => uc.User == “admin”), // outer sequence 
c => new { c.CompanyId, c.CustomerId }, // inner key selec­tor 
uc => new { uc.CompanyId, uc.CustomerId }, // outer key selec­tor 
(c, uc) => c); 

这两种方法都会得到相同的结果（客户的公司标识为“AC”，客户标识为“Customer1”），但正如您所看到的，lambda表达式更难以书写和阅读！

希望这会有所帮助！