【LINQ 查询】
2016-10-24
事例：
先定义两个类Master和KongFu，然后在这两个类中定义变量
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1 class Master 2 { 3 publicintId{ get;set;} 4 publicstringName{ get;set;} 5 publicintAge{ get;set;} 6 publicstringKongfu{ get;set;} 7 publicstringMenPai{ get;set;} 8 publicintLevel{ get;set;} 9 public overide string ToString() 10 { 11 return string.Fromat("Id:{0},Name:{1},Age:{2},Kongfu:{3},MenPai:{4},Level:{5}", Id, Name, Age, Kongfu, Menpai, Leve) 12 } 13 }1 class KongFu 2 { 3 public int Id { get;set;} 4 public string Name { get;set;} 5 public int Power { get;set;} 6 7 public override string ToString() 8 { 9 return string.Format("Id:{0},Name:{1},Power:{2}", Id, Name, Power); 10 } 11 }1 static void Main(String[] args) 2 { 3 var master =newList<Master>() 4 { 5 newMaster(){Id=1,Name="黄蓉",Age=18,Menpai="丐帮", Kongfu="打狗棒法",Level=9}, 6 newMaster(){Id=2,Name="洪七公",Age=70,Menpai="丐帮", Kongfu="打狗棒法",Level=10}, 7 newMaster(){Id=3,Name="郭靖",Age=22,Menpai="丐帮", Kongfu="降龙十八掌",Level=10}, 8 newMaster(){Id=4,Name="任我行",Age=50,Menpai="明教", Kongfu="葵花宝典",Level=1}, 9 newMaster(){Id=5,Name="东方不败",Age=35,Menpai="明教", Kongfu="葵花宝典", Level=10}, 10 newMaster(){Id=6,Name="林平之",Age=23,Menpai="华山", Kongfu="葵花宝典", Level=7}, 11 newMaster(){Id=7,Name="岳不群", Age=50,Menpai="华山",Kongfu="葵花宝典",Level=8}, 12 newMaster(){Id=8,Name="令狐冲",Age=23,Menpai="华山",Kongfu="独孤九剑", Level=10}, 13 newMaster(){Id=9,Name="梅超风",Age=23,Menpai="梅花岛",Kongfu="九阴真经", Level=10}, 14 newMaster(){Id=10,Name="黄药师",Age=23,Menpai="梅花岛",Kongfu="弹指神功",Level=10}, 15 newMaster(){ Id = 11, Name = "风清扬", Age = 23, Menpai = "华山", Kongfu = "独孤九剑", Level = 10 } 16 }; 17 var kongfu =newList<KongFu>() 18 { 19 newKongFu(){Id=1,Name="打狗棒法", Power=95 }, 20 newKongFu(){Id=2,Name="降龙十八掌",Power=100}, 21 newKongFu(){Id=3,Name="葵花宝典", Power=100}, 22 newKongFu(){Id=4,Name="独孤九剑", Power=100}, 23 newKongFu(){Id=5,Name="九阴真经", Power=100}, 24 newKongFu(){Id=6,Name="弹指神功", Power=100}, 25 }; 26 }
开始建立查询：
【第一种】：找出Level大于8的列表来
var result = new List<Master>();
foreach (var item in master)
{
if (item.Level > 8)
{
result.Add(item);
}
}
foreach (var item in result)
{
Console.WriteLine(item.ToString());//ToString()不写默认存在
}
Console.ReadKey();
//需要在 master类和KongFu中创建 ToString()方法，因为在查询完以后进行遍历（foreach）的时候h会出现以下错误
【第二种】：利用专业查询语言查找并排序
//from：表示从哪个集合里查找……where：查新条件……select：返回结果列表
var result2 = from m in master
where m.Level < 10//查询条件
orderby m.Level//根据level进行升序排序
orderby m.Level descending//根据level进行降序排序
select m;
foreach (var item in result2)
{
Console.WriteLine(item);
}
Console.ReadKey();
【按条件查找并排序】
var ressult22 = from m in master.Where(m => m.Level < 10).OrderBy(m => m.Age)//OrderBy && OrderByDescending 升序和降序 排列
select m;
foreach (var item in ressult22)
{
Console.WriteLine(item);
}
Console.ReadKey();
【第三种】：调用函数的方法来实现查找功能
var result3 = master.Where(T1);
foreach (var item in result3)
{
Console.WriteLine(item);
}
Console.ReadKey();
//需要调用的类
static bool T1(Master m)
{
if (m.Level < 10)
{ return true; }
else
{ return false; }
}
【第四种】：利用lamada表达式查找
var result4 = master.Where(m => m.Level < 10);//lamada表达式 参数名=>表达式
foreach (var item in result4)
{
Console.WriteLine(item);
}
Console.ReadKey();
【第五种】：将两个列表联合起来，形成 Count(master) * Count(Kongfu) 的列表
var result5 = from m in master
from f in kongfu
select new { mm = m, ff = f };//
foreach (var item in result5)
{
Console.WriteLine(item);
}
Console.ReadKey()
【第六种】：查询当 master.Level == Kongfu.Id，时两个的信息
var result6 = from m in master
from f in kongfu
//where m.Level == f.Id
where m.Kongfu == f.Name && f.Power > 90
select new { mm = m, ff = f };
foreach (var item in result6)
{
Console.WriteLine(item);
}
Console.ReadKey();
【第七种】：实现master和Kongfu中属性相等的信息输出
var result7 = from m in master
//将kongfu列表中的信息放入k中，选出 m.Kongfu == k.Name的信息
join k in kongfu on m.Kongfu equals k.Name
select new { mm = m, kk = k };
foreach (var item in result7)
{
Console.WriteLine(item);
}
Console.ReadKey();
【第八种】：一人修炼一门功夫，一门功夫被多少人修炼
var result8 = from k in kongfu
join m in master on k.Name equals m.Kongfu
into groups//把武林高手分类，看看哪门功夫被人修炼的多
orderby groups.Count()//按照修炼人进行
select new { kongfu = k, count = groups.Count() };//groups.count：获取到
foreach (var item in result8)
{
Console.WriteLine(item);
}
Console.ReadKey();
//将修炼功夫一样的人放在一起并输出master和kongfu的信息
var result = from k in kongfu
join m in master on k.Name equals m.Kongfu
select new { mm = m, kk = k };
foreach (var item in result)
{
Console.WriteLine(item);
}
Console.ReadKey();
【第九种】：按照自身帮派进行分组，
var result9 = from m in master
group m by m.Menpai//将门派分组，放到m中
into p//表示放到p中
select new { count = p.Count(), key = p.Key };//count = p.Count()表示这组有多少人
//key = p.Key表示这个是按照什么分的，即关键字"Key"为Menpai
foreach (var item in result9)
{
Console.WriteLine(item);
}
Console.ReadKey();
【第十种】：确定序列中元素是否满足条件
Any在内部循环遍历每个元素
根据m=>m.Menpai判断是否满足条件
bool result10 = master.Any(m => m.Menpai == "丐帮");
Console.WriteLine(result10);
Console.ReadKey();
时间： 2024-12-10 10:36:56