以前一直用 var query = xxx.Select(c=>new {c.X,c.Y}); 來取表中的某二列字段，今天有個應用需要轉成Dictionary<T,U>，很少這樣使用，居然忘記了寫法！

?

回憶了半天終于寫對了，貼在這里備個份，方便以后查找:

using?System;
using?System.Collections.Generic;
using?System.Linq;

namespace?DicTest
{
????class?Program
????{
????????static?void?Main(string[]?args)
????????{
????????????List<Test>?lst?=?new?List<Test>();
????????????for?(int?i?=?0;?i?<?10;?i++)
????????????{
????????????????lst.Add(new?Test()?{?Id?=?Guid.NewGuid(),?Num?=?i,?Name?=?i.ToString()?});
????????????}

????????????Dictionary<Guid,?int>?dic?=?lst.ToDictionary(new?Func<Test,?Guid>(c?=>?c.Id),?new?Func<Test,?int>(c?=>?c.Num)); //如果覺得上面的寫法太復雜，還可以簡化為 //?Dictionary<Guid, int> dic = lst.ToDictionary(c => c.Id, c => c.Num);　　

????????????foreach?(Guid?Id?in?dic.Keys)
????????????{
????????????????Console.WriteLine("Key:{0}\tValue:{1}",?Id,?dic[Id]);
????????????}

????????????Console.Read();
????????}
????}


????public?class?Test
????{
????????public?Guid?Id?{?set;?get;?}
????????public?int?Num?{?set;?get;?}
????????public?string?Name?{?set;?get;?}
????}
}

?

如果用Reflector反射一下，會發現實際上編譯器自動生成了類似以下代碼:(部分名稱做了友好處理)?

代碼 [CompilerGenerated]
private?static?Func<Test,?Guid>?funcGuid;
?
[CompilerGenerated]
private?static?Func<Test,?int>?funcInt;
?
[CompilerGenerated]
private?static?int?mNum(Test?c)
{
????return?c.Num;
}
?
[CompilerGenerated]
private?static?Guid?mId(Test?c)
{
????return?c.Id;
}


private?static?void?Main(string[]?args)
{
????List<Test>?lst?=?new?List<Test>();
????for?(int?i?=?0;?i?<?10;?i++)
????{
????????Test?_t?=?new?Test();
????????_t.Id?=?Guid.NewGuid();
????????_t.Num?=?i;
????????_t.Name?=?i.ToString();
????????lst.Add(_t);
????}
????Dictionary<Guid,?int>?dic?=?lst.ToDictionary<Test,?Guid,?int>((funcGuid?!=?null)???funcGuid?:?(funcGuid?=?new?Func<Test,?Guid>(Program.mId)),?(funcInt?!=?null)???funcInt?:?(funcInt?=?new?Func<Test,?int>(Program.mNum)));
????foreach?(Guid?Id?in?dic.Keys)
????{
????????Console.WriteLine("Key:{0}\tValue:{1}",?Id,?dic[Id]);
????}
????Console.Read();
}

?

?

PS:今天寫的好象都是些水文 :)

轉載于:https://www.cnblogs.com/yjmyzz/archive/2009/12/04/1617240.html

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