C#学习笔记——LINQ数据访问

1)查询表达式

static void Main(string[] args)
{
string[] strName = new string[] { "asdfsdfsdds","dsaffsdfa","df"};
IEnumerable<string> selectQuery =       //IEnumerable接口：公开枚举数，支持在非泛型集合上进行迭代
from Name in strName                //选出长度小于6的所有项
where Name.Length < 6
select Name;
foreach(string str in selectQuery)
{
Console.WriteLine(str);
}
Console.ReadLine();
}

2）用from语句指定数据源

static void Main(string[] args)
{
string[] values = { "aaa","bbb","ccc"};
var value = from v in values             //var类似于object，使用var必须定义时初始化，初始化完成，不能再给变量赋与初始化值类型不同的值
select v;
Console.WriteLine("result:");
foreach(var v in value)
{
Console.WriteLine(v.ToString()+"  ");
}
Console.ReadLine();
}

3)用where子句指定筛选条件

static void Main(string[] args)
{
int[] values = { 1,2,3,4,5,6,7,8,9,0};
var value = from v in values
where v % 2 == 0 && v > 2
select v;
Console.WriteLine("results:");
foreach (var v in value)
{
Console.WriteLine(v.ToString()+" ");
}
Console.ReadLine();
}

4)用orderby子句进行排序

static void Main(string[] args)
{
int[] values = { 3,6,7,4,2,8,0,1,9,5};
var value = from v in values
where v &
4000
lt; 3 || v > 7
orderby v descending
select v;
Console.WriteLine("results:");
foreach(var v in value)
{
Console.WriteLine(v + " ");
}
Console.ReadLine();
}