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Linq

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Linq语句

 

Linq查询表达式以from开头select或group结尾

2021-09-06
          


7


 
 

 



 
 

1


from :指定查询操作的数据源和范围变量




2


join :连接多个用于查询操作的数据源  , 输出相同的值




3


into :提供一个临时标识符，join子句，group子句，或select子句均可以通过该标识符引用查询操作的中间结果




4


let  :引入用来临时保存查询表达式中的字表达式结果的范围变量




5


where:指定筛选元素的逻辑条件




6


orderby:对查询结果进行顺序操作，包括升序和降序




7


select:指定查询结果的类型和表现形式







 
 




代码



 
 
 
 
 









143


 
 

 



 
 

1


using System;




2


using System.Linq;




3






4


namespace Linq




5


{




6


    class Program




7


    {




8


        static bool Bl(int a) 




9


        {




10


            return a % 2 == 0 ? true : false;




11


        }




12






13


        static void Main(string[] args)




14


        {




15


            int[] Array = { 1, 2, 4, 5, 6, 7, 8 };




16






17


            var La = from a in Array




18


                     select a;




19






20


            var La2 = from a in Array




21


                      where a < 2




22


                      select a;




23






24


            foreach (var a in La)




25


                Console.WriteLine("La = " + a);




26






27


            foreach (var a in La2)




28


                Console.WriteLine("La2 = " + a);




29






30


            Console.WriteLine("L2第一个元素 = " + La2.First());




31






32


            //两个数组相加，




33


            int[] A1 = { 1, 2, 3, 4, 5, 6, 7, 8 };




34


            int[] A2 = { 1, 2, 3, 4, 5, 6, 7, 8 };




35


            var Lin = from a1 in A1




36


                      from a2 in A2




37


                      select a1 + a2;




38






39


            foreach (var item in Lin)




40


            {




41


                Console.Write(item + "  ");




42


            }




43






44


            //给结果值添加名称：i=1 ， name = 1




45


            int[] A3 = { 1, 2, 3, 4, 5, 6, 7, 8 };




46


            var Lin2 = from a1 in A3




47


                       select new




48


                       {




49


                           i = a1,




50


                           name = a1.ToString()




51


                       };




52


            foreach (var L in Lin2)




53


            {




54


                Console.WriteLine("Lin2 = " + L);




55


            }




56






57


            //对每个值乘10




58


            int[] A4 = { 1, 2, 3, 4, 5, 6, 7, 8 };




59


            var Lin3 = from a in A4




60


                       select a * 10;




61


            Console.WriteLine("Lin3 = " + Lin3.First());




62






63


            //where判断语句




64


            int[] A5 = { 1, 2, 3, 4, 5, 6, 7, 8 };




65


            var Lin4 = from a in A5




66


                       where a > 7




67


                       select a;




68






69


            //判断是偶数还是奇数,偶数显示奇数不显示




70


            int[] A6 = { 1, 2, 3, 4, 5, 6, 7, 8 };




71


            var Lin5 = from a in A6




72


                       where Bl(a)




73


                       select a;




74


            foreach (var i in Lin5)




75


            {




76


                Console.WriteLine("判断语句包含函数 =   " + i);




77






78


            }




79






80


            //let语句， n = a % 2 （=偶数） ，where n == 0 （=偶数）  




81


            int[] A7 = { 1, 2, 3, 4, 5, 6, 7, 8 };




82


            var Lin6 = from a in A7




83


                       let n = a % 2




84


                       where n == 0




85


                       select a;




86


            foreach (var item in Lin6)




87


            {




88


                Console.WriteLine(" let语句 =   " + item);




89


            }




90






91


            //降序或升序




92


            var Lin7 = from a in A7




93


                       orderby a descending //ascending




94


                       select a;




95


            foreach (var item in Lin7)




96


            {




97


                Console.WriteLine(" 升序或降序 =    " + item);




98


            }




99






100


            //group  by  分组语句




101


            var Lin8 = from a in A7




102


                       group a by a % 2;




103






104


            foreach (var i in Lin8)




105


            {




106


                foreach (var j in i)




107


                {




108


                    Console.WriteLine("group分组语句 =   " + j);




109






110


                }




111


            }




112






113


            //group and into




114






115


            var Lin9 = from a in A7




116


                       group a by a % 2 into Aa




117


                       from InTo in Aa




118


                       select InTo;




119






120


            foreach (var i in Lin9)




121


            {




122


                Console.WriteLine("group and into =   " + i);




123


            }




124






125


            // join语句,连接两个数组，判断Array1和Array2相同的值




126






127


            int[] Array1 = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };




128


            int[] Array2 = { 1, 78, 3, 4, 5, 84, 7, 8, 98 };




129






130


            var Query = from a in Array1




131


                        join b in Array2 on a equals b




132


                        select a;




133






134


            foreach (var i in Query)




135


            {




136


                Console.WriteLine("Join =   "+i);




137


            }




138






139






140


        }




141


    }




142


}




143









 
 






深入_SelectMany();  存在多个from语句时使用




 
 
 
 
 









24


 
 

 



 
 

1


            //常规方法-------------------------------------




2


var Linq2 = from a in _Name




3


            from b in _Birth




4


            where a.height < b.Min_Height




5


            orderby a.Id




6


            select "姓名： " +a.Name+ " 年龄： "+a.Age + " 体重： "+a.Weight + " 身高： "+a.height + " 最低身高： "+b.Min_Height + " 最低体重 "+b.Max_Height + "\n";




7






8


            Console.WriteLine("不符合条件的有：");




9


            foreach (var item in Linq2)




10


            {




11


                Console.WriteLine(item);




12


            }




13






14


//SelectMany()  --------使用方式------------------------------




15


            var Linq2_J = _Name.SelectMany(B => _Birth, (N, B) => new { n = N, b = B })




16


                .Where(N => N.n.height < N.b.Min_Height)




17


                .OrderBy(N => N.n.Id)




18


                .Select(N=> "姓名： " + N.n.Name + " 年龄： " + N.n.Age + " 体重： " + N.n.Weight + " 身高： " + N.n.height + " 最低身高： " + N.b.Min_Height + " 最低体重 " + N.b.Max_Height + "\n");




19






20


            Console.WriteLine("不符合条件的有：");




21


            foreach (var item in Linq2_J)




22


            {




23


                Console.WriteLine(item);




24


            }







 
 






 
 
 
 
 









25


 
 

 



 
 

1


            //方法1-----------------------------------




2


var i = 1;




3


            var Linq3 = from a in _Name




4


                        from b in _Birth




5


                        where a.Kungfu == b.Kungfu




6


                        orderby a.ko * b.ko descending, a.Age, a.Name




7


                        select "Id: " + a.Id + " 姓名： " + a.Name + " 所练功夫： " + a.Kungfu + " 排位： " + (i++);




8


            Console.WriteLine("全武林武力值排行榜：");




9


            foreach (var item in Linq3)




10


            {




11


                Console.WriteLine(item);




12


            }




13


//方法2----------------------------------------------------------




14


            i = 1;




15


            var Linq3_J = _Name.SelectMany(B => _Birth, (N, B) => new { n = N, b = B })




16


                .Where(C => C.n.Kungfu == C.b.Kungfu)




17


                .OrderByDescending(C => C.n.ko * C.b.ko)




18


                .ThenBy(C => C.n.Name)




19


                .Select(C=>"ID= "+ C.n.Id+" 姓名： "+C.n.Name+" 所练功夫： "+C.n.Kungfu+"武力值：" + (C.n.ko * C.b.ko) + " 排位: "+(i++));




20






21


            Console.WriteLine("全武林武力值排行榜：");




22


            foreach (var item in Linq3_J)




23


            {




24


                Console.WriteLine(item);




25


            }







 
 




SelectMany()


Join语句



 
 
 
 
 









22


 
 

 



 
 

1


int J = 1;




2


            var Linq4 = from a in _Birth




3


                        where a.ko > 60




4


                        orderby a.ko descending




5


                        select new {id = a.Id,kungfu = a.Kungfu,ko=a.ko,top = (J++) };




6


            int Ji = 1;




7


            var Linq4_J = _Name.Where(b => b.ko > 6)




8


                                .OrderByDescending(b => b.ko)




9


                                .Select(b=>new {id=b.Id,name = b.Name,ko = b.ko ,kungfu = b.Kungfu ,top = (Ji++) });




10


//连接两个对象进行比较胜负




11


            int Jii = 1;




12


            var Linq5 = from a in Linq4




13


                        join b in Linq4_J on a.kungfu equals b.kungfu




14


                        orderby a.ko * b.ko descending




15


                         select new { id = b.id, name = b.name, ko = (a.ko * b.ko)




16


                        ,kungfu = a.kungfu,Birth = a.top, name_top = b.top, top = Jii++};




17


//方法二：使用拓展方法




18


int Jiii = 1;




19


            var Linq5_J = Linq4.Join(Linq4_J, a => a.kungfu, b => b.kungfu, (A, B) =>




20


            new { id = B.id, name = B.name, ko = (B.ko * A.ko), kungfu = A.kungfu, 




21


                    Birth = A.top, name_top = B.top, top = (Jiii++) })




22


            .OrderByDescending(m=>m.ko);







 
 




Join


对武林功夫进行排序,此方法是透过count计数排序,判断该武功有多少人使用，从而做到分组



 
 
 
 
 









19


 
 

 



 
 

1


            //Linq




2


            var Linq6 = from a in _Birth




3


                        join b in _Name on a.Kungfu equals b.Kungfu into Groups




4


                        orderby Groups.Count() descending




5


                        select new {Id = a.Id , Kungfu = a.Kungfu , ko = a.ko ,count = Groups.Count() };




6


            Console.WriteLine("功夫使用人数分组：");




7


            foreach (var item in Linq6)




8


            {




9


                Console.WriteLine("ID: "+item.Id+" 功夫： "+item.Kungfu+" 武力值： "+item.ko +" 此武功使用人数： "+item.count );




10


            }




11






12


            //拓展方法




13


            var Linq6_J = _Birth.GroupJoin(_Name, A => A.Kungfu, B => B.Kungfu, (A, B) => new { A.Id, A.Kungfu, A.ko, count = B.Count() })




14


                .OrderByDescending(C=>C.count);




15


            Console.WriteLine("功夫使用人数分组：");




16


            foreach (var item in Linq6_J)




17


            {




18


                Console.WriteLine("ID： "+item.Id+" 功夫： "+item.Kungfu+" 武力值： "+item.ko+" 此功夫使用人数： "+item.count );




19


            }







 
 




GroupJoin()


对武林武功进行排序，此方法是透过id安id大小排序做到分组



 
 
 
 
 









20


 
 

 



 
 

1


//Linq语句




2


var Linq7 = from a in _Birth




3


            join b in _Name on a.Kungfu equals b.Kungfu




4


            orderby a.Id




5


            select new { Id = a.Id, name = b.Name, Kungfu = a.Kungfu, ko = (a.ko * b.ko) };




6






7


            Console.WriteLine("joinorGroup分组");




8


            foreach (var item in Linq7)




9


            {




10


                Console.WriteLine("Id= " + item.Id + " 姓名： " + item.name + " 所练功夫： " + item.Kungfu + " 武力值： " + item.ko);




11


            }




12


//拓展方法




13


            var Linq7_J = _Birth.GroupJoin(_Name, A => A.Kungfu, B => B.Kungfu, (A, B) => new { Id = A.Id, count = B.Count(), Kungfu = A.Kungfu })




14


                                .OrderBy(m=>m.Id);




15






16


            Console.WriteLine("joinorGroup分组");




17


            foreach (var item in Linq7_J)




18


            {




19


                Console.WriteLine("Id= " + item.Id  + " 所练功夫： " + item.Kungfu+" 使用人数： "+item.count);




20


            }







 
 




Group分组武功，linq与Groupby();



 
 
 
 
 









19


 
 

 



 
 

1


            //linq语句




2


var Linq8 = from a in _Name




3


                        group a by a.Kungfu into b




4


                        orderby b.Key




5


                        select new {kungfu = b.Key,count = b.Count() };




6






7


            Console.WriteLine("分组个各武功使用数");




8


            foreach (var item in Linq8)




9


            {




10


                Console.WriteLine("功夫名： "+item.kungfu+" 使用人数： "+item.count);




11


            }




12


//拓展方法




13


            var Lin8_J = _Name.GroupBy(a=>a.Kungfu,(A,B)=>new {kungfu =A,count = B.Count() })




14


                                .OrderBy(m=>m.kungfu);




15


            Console.WriteLine("分组个各武功使用数");




16


            foreach (var item in Lin8_J)




17


            {




18


                Console.WriteLine("功夫名： " + item.kungfu + " 使用人数： " + item.count);




19


            }







 
 





判断对象里面是否包含指定内容 变量.Any();



 
 
 
 
 









2


 
 

 



 
 

1


bool lbwb = Lin8_J.Any(v=>v.kungfu == "凌波微步");//判断对象是否包含用凌波微步的人




2


            Console.WriteLine("是否含有使用凌波微步的人："+lbwb);//返回布尔值







 
 



判断是否所有对象都一致： 变量.All();


 
 
 
 
 









2


 
 

 



 
 

1


bool xlsbz = Lin8_J.All(v=>v.kungfu == "降龙十八掌");




2


            Console.WriteLine("所有人都使用降龙十八掌："+xlsbz);







 
 



判断对象里面是否包含某个对象


 
 
 
 
 









3


 
 

 



 
 

1


var QiaoFeng = _Name[5]; 




2


            bool IsQiaoFeng = _Name.Contains(QiaoFeng);//判断某对象是否存在




3


            Console.WriteLine("江湖中是否存在乔峰这个人："+IsQiaoFeng);







 
 



算出对象总数和页码


 
 
 
 
 









1


 
 

 



 
 

1









 
 



分页


 
 
 
 
 









11


 
 

 



 
 

1


            double Page = 10;//每页数量




2


            int name_count = _Name.Count();//对象总数




3


            double count = Math.Ceiling(name_count / Page);//计算总共有多少页




4


            Console.WriteLine("当前对象总页数："+count+" 当前对象总数："+ name_count);




5






6


            var Linq9 = (from a in _Name




7


                         join b in _Birth on a.Kungfu equals b.Kungfu




8


                         orderby a.ko * b.ko descending




9


                         select new { name = a.Name, Kungfu = b.Kungfu, ko = a.ko * b.ko })




10


                         .Skip(0 * (int)Page)     // 0 *Page = 第一页，以此类推




11


                         .Take((int)Page);        // 返回指定数量（Page）元素







 
 



对比两个值返回值相同的集合


 
 
 
 
 









9


 
 

 



 
 

1


//如果功夫为 降龙十八掌 和武力值为 10 就能返回




2


var Linq10 =(from a in _Name where a.Kungfu == "降龙十八掌" select a)




3


            .Intersect(from b in _Name where b.ko == 10 select b);//Intersect:返回比较值相同的集合




4






5


            Console.WriteLine("\n比较两个值返回值相同的集合：");




6


            foreach (var item in Linq10)




7


            {




8


                Console.WriteLine(" 姓名 "+item.Name+" 功夫 "+item.Kungfu +" 等级 "+item.ko);




9


            }







 
 



累加：Aggregate


 
 
 
 
 









5


 
 

 



 
 

1


            int[] array = { 1,2,3,4,5,6};




2


            int arr1 = array.Aggregate((a,b)=>a+b);                     //Aggregate累加 最后结果=21




3


            int arr2 = array.Aggregate(0,(a,b)=>a+b , r=>r*2);         //Aggregate累加 最后结果=42




4


            int arr3 = array.Aggregate(9,(a,b)=>a+b);                 //Aggregate累加 最后结果=30




5


            Console.WriteLine(arr1 +" "+ arr2 + " " + arr3);







 
 




 
linq模糊查询


 
 
 
 
 









57


 
 

 



 
 

1


1.判断是否为空或者null




2






3


string.IsNullOrEmpty(des.PlateNum)————————>sql server的PlateNum is null的判断




4






5


from des in db.ModelsVehicleRecognition where (!string.IsNullOrEmpty(des.PlateNum)) select new { plateMun = des.PlateNum }




6






7


等同于




8






9


SELECT PlateNum FROM VehicleRecognition WHERE PlateNum IS NOT NULL




10






11


2.普通包含模糊查询




12






13


1）以某字符串开头的模糊查询




14






15


des.PlateNum.StartsWith("皖A8") ————————>sql server 的   like '皖A8%'




16






17


from des in db.ModelsVehicleRecognition where (des.PlateNum.StartsWith("皖A8")) select new { plateMun = des.PlateNum }




18






19


等同于




20






21


SELECT PlateNum FROM VehicleRecognition WHERE PlateNum  like '皖A8%'




22






23


2）以某字符串结尾的模糊查询




24






25


des.PlateNum.EndsWith("68T") ————————>sql server 的   like '%68T'




26






27


from des in db.ModelsVehicleRecognition where (des.PlateNum.EndsWith("68T")) select new { plateMun = des.PlateNum }




28






29


等同于




30






31


SELECT PlateNum FROM VehicleRecognition WHERE PlateNum  like '%68T'




32






33


3）包含某字符串的模糊查询




34






35


des.PlateNum.Contains("A3") ————————>sql server 的   like '%A3%'




36






37


from des in db.ModelsVehicleRecognition where (des.PlateNum.Contains("A3")) select new { plateMun = des.PlateNum }




38






39


等同于




40






41


SELECT PlateNum FROM VehicleRecognition WHERE PlateNum  like '%A3%'




42






43


3.精确到字符串对应位数字符的模糊查询（*重点）




44






45


SqlFunctions.PatIndex("_a__3%", des.PlateNum) > 0————————>sql server 的   like '_a__3%'




46






47


from des in db.ModelsVehicleRecognition where (SqlFunctions.PatIndex("_a__3%", des.PlateNum) > 0) select new { plateMun = des.PlateNum }




48






49


等同于




50






51


SELECT PlateNum FROM VehicleRecognition WHERE PlateNum  like '_a__3%'




52






53


说明：'_a__3%' 中的下划线“_”表示一个字符，'_a__3%' 这个字符串查询意思就是第二个字符是a,第五个字符是3的字符串




54






55


       因为a和3之间有两个下划线“_”所以查询出的结果也要满足a和3之间有两个字符才行，




56






57


       也就是说两个精确字符之间隔了几个字符，在查询的时候就要写几个下划线“_”。

                    

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