将此LINQ表达式转换为Lambda

要将Linq查询转换为其Lambda等价项,请执行以下操作:

1. 下载 Linqpad 跑你的车 查询
2. 在结果窗口中,单击 在工具栏的“”按钮上。 就在结果窗口的正上方
3. 您的查询将转换为 Lambda表达式等价物!

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

以下是我遵循的启发:

当有连接时,喜欢LINQ表达式而不是lambdas。

    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ReSharper的convert LINQ to method chain选项,等于以下值:

        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)
                                    });

以下是如何使用lambda编写此查询:

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);

这两种方法都会产生相同的结果(公司Id为AC的客户和客户Id为Customer1的客户),但正如您所看到的,lambda表达式更难编写和读取!

希望这有帮助!

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