ADO.NET 4 快速上手（10）——LinQ

十、    LinQ

1.    LinQ

string[] names = new string[] {
    "n1", "n2", "n3", "n4", "n5", "n6"};
int[] ages = new int[] {
    10, 20, 30, 40, 50, 60};

// 投影
var results1_1 = from n in names select n;
var results1_2 = names.Select(n => n);
// 匿名
var results2 = from n in names select new {Upper = n.ToUpper(), Length = n.Length};

// 篩選
var results3 = from n in names where n.EndsWith("3") select n;
var results4 = names.Where(n => n.EndsWith("3"));

// 排序
var results5 = from n in names orderby n descending select n;
var results6 = names.OrderByDescending(n => n);

// 鏈接
var results7 = from n in names 
                from a in ages
                where int.Parse(n[1].ToString()) == a / 10

2.    LinQ to DataSet

DataTable table = new DataTable();
table.Columns.Add("name");
table.Columns.Add("age");
table.Rows.Add(new object[] {"Jack", 20});
table.Rows.Add(new object[] {"Ang", 22 });

var results = from u in table.AsEnumerable() select u;

Console.WriteLine(results.FirstOrDefault()["name"]);

3.    LinQ to Entities

using (UserEntities context = new UserEntities())
{ 
    var results = from u in context.tb_User select u;
    Console.WriteLine(results.FirstOrDefault().Username);
}