Linq To List 集合查询 - c++编程基础

//Linq对集合的各种查询
public static void Run()
{
List customerlist = new List ();
customerlist.Add(new Customers() { id = 1, Name = "Jack", Custom = "Mis" });
customerlist.Add(new Customers() { id = 2, Name = "Lus", Custom = "Google" });
customerlist.Add(new Customers() { id = 3, Name = "Qiao", Custom = "Baidu" });
customerlist.Add(new Customers() { id = 4, Name = "Qiao", Custom = "Apple" });
customerlist.Add(new Customers() { id = 5, Name = "Adb", Custom = "Adobe" });

//简单的查询
var customerQuery = from query in customerlist
select query;

//带where筛选
var customerWhereQuery = from query in customerlist
where query.id == 1 && query.Name == "Lus"
select query;

//排序Ordering
var customerOrderingQuery = from query in customerlist
where query.Name == "Lus"
orderby query.id ascending
select query;

//分组Group by
var customerGroupbyQuery = from query in customerlist
group query by query.Name;
//可以使用into进一步查询
var customerGroupbyIntoQuery = from query in customerlist
group query by query.Name into queryGroup
where queryGroup.Key == "Qiao"
select queryGroup;

//联接查询 join 子句始终针对对象集合而非直接针对数据库表运行。
List customerJoinlist = new List ();
customerJoinlist.Add(new Customers() { id = 1, Name = "Jack", Custom = "Mis" });
customerJoinlist.Add(new Customers() { id = 2, Name = "Lus", Custom = "Google" });
customerJoinlist.Add(new Customers() { id = 3, Name = "Qiao", Custom = "Baidu" });
var customerJoinQuery = from query1 in customerlist
join query2 in customerJoinlist
on query1.id equals query2.id
select new { CustomerName = query1.Name, CustomerName2 = query2.Name };

//数据源的类型参数始终为查询中的范围变量的类型。
//比如List 类型为Customers 在循环迭代的时候类型必须可以隐式转换为Customer 有一种情况是
//这种情况下Customers类型转换为了String ..在select query.Name已经将查询目标类型定位了String类型
var customerTypeQuery = from query in customerlist
where query.Name == "Lus"
select query.Name;

//结合Lamdba对List集合筛选(s => s.Name == "Qiao")
List listString = customerlist.Where(s => s.Name == "Qiao").ToList();

}
}

public class Customers
{
public int id { get; set; }

public string Name { get; set; }

public string Custom { get; set; }
}