List操作之Select

本文是寫給C#新手，老手就勿看了，講的實際上就是LINQ，謝謝一樓的提醒。

很多時候，從一個關系表中挑出一個我們需要的元素列表采用SQL語句是再容易不過的了，其實C#的List中也可以采用類似的方法，雖然List中集成了Select(), Where()等語句，不過如果你的判斷規則較為復雜，或者想要看起來一目了然，以下的方法也是可行的：

首先假設你有一個類

public class People
{
    public string Name { get; set; }
    public int Age { get; set; }
}

並且有一些初始化語句

List<People> PeopleList = new List<People>();
PeopleList.Add(new People() { Name = "Haocheng Wu", Age = 24 });
PeopleList.Add(new People() { Name = "Haocheng Wu", Age = 25 });
PeopleList.Add(new People() { Name = "James Wu", Age = 23 });

你就可以采用下面類似於SQL語句的方法進行select

List<string> SubPeopleNameList1 = (from people in PeopleList
                              where people.Name == "Haocheng Wu" && people.Age == 24
                              select people.Name).ToList<string>();

當然你也可以用一行代替

 

List<string> SubPeopleNameList2 = PeopleList.Where(people => people.Name == "Haocheng Wu" && people.Age == 24).Select(people => people.Name).ToList();

不過顯然第一種方法更加一目了然，尤其是當判斷條件相當復雜的時候就更加有用了