你的位置:首页 > ASP.net教程

[ASP.net教程]Linq学习总结1


2个要点:

1.linq操作的集合必须实现IEnumerable接口,所以在这3.0之前为实现该接口的集合需通过Cast或TypeOf方法转换成可Linq的集合;

2.查询式和Lame那啥表达式都可以一起使用.那个方便用哪个,他们只在第一次使用时才会真正去查询;

 

  List<Employee> ils = new List<Employee>()       {         new Employee(){IDCode="jack5",Age=20,littleName="ab"},        new Employee(){IDCode="mike444",Age=12,littleName="aa"},        new Employee(){IDCode="mary5",Age=12,littleName="zs"},        new Employee(){IDCode="sm5555",Age=67,littleName="yb"},        new Employee(){IDCode="som",Age=67,littleName="cr"}      };      ArrayList als = new ArrayList()       {        new Department(){Name="jack",DepName="富士康"},        new Department(){Name="jack",DepName="華為"},        new Department(){Name="mary",DepName="騰訊"},        new Department(){Name="sum",DepName="移動"},        new Department(){Name="soom",DepName="聯通"}      };      #region 查詢語句 第三章,linq技術詳解      //帶有Into的group by語句      var va = from c in ils           group c by new { c.littleName, c.Age } into g           select new { Name = g.Key, ageC = g.Count() };      var va1 = ils.GroupBy(p => new { p.littleName, p.Age }).Select(p => new { name = p.Key, agec = p.Count() });      //顯示枚舉變量類型      var varT = from c in ils            join Department d in als on c.IDCode equals d.Name            select new { age = c.Age, depName = d.DepName };      var varT1 = ils.Join(als.Cast<Department>(), c => c.IDCode, p => p.Name, (c, p) => new { age = c.Age, depName = p.DepName });      //join語句      var varJoin = from c in ils             join Department d in als             on c.IDCode equals d.Name             into ao             select new { c.IDCode, sum = ao.Sum(p => p.DepName.Length) };      var varJoin1 = ils.GroupJoin(als.Cast<Department>(), a => a.IDCode, b => b.Name, (b, a) => new { b.IDCode, sum = a.Count() });      //Let和Where語句      var varLet = from c in ils             let names = c.IDCode + ":" + c.littleName             where names.Length > 5             select new { c.Age, names };      var varLet1 = ils.Select(a => new { a, names = a.IDCode + ":" + a.littleName })        .Where(p => p.names.Length > 5)        .Select(b => new { b.a.Age, b.names });      //Generator語句(多個 from),orderby語句      var varSelMany = from a in ils               from b in als.Cast<Department>()               orderby a.Age, a.Department descending               select new { a.IDCode, a.littleName, a.Age, b.DepName };      var varSelMany1 = ils.SelectMany(p => als.Cast<Department>().Select(a => new { p.Age, a.DepName })).OrderByDescending(a => a.Age).ThenByDescending(a => a.DepName);      //group by      var varGroup = from p in ils              group p by p.Age                into a                select a.Key + ":" + als.Capacity;            #endregion      #region 延遲操作符詳解      //異常都是ArgumentNullException      //select,where都有兩個原型,另一個原型有索引參數      var varWhere = ils.Where((p, i) => i < 2);      //分區操作符 take      var varTake = ils.Take(2);      //TakeWhile 只要條件不符合就會跳出      var varTakeWhile = ils.TakeWhile((p, q) => p.IDCode.Length > 4);      //skip 與take互補      var varSkip = ils.Skip(2);      //skipwhile 與takewhile互補      var varSkipWhile = ils.SkipWhile((a, i) => a.IDCode.Length > 5 && i < 3);      //串聯操作符      var varConcat = ils.Take(2).Concat(ils.Skip(2));      //concat只可以串聯兩個序列,當串聯多個序列的時候可以用SelectMany;      var varSelectMany1 = new[] { ils.Take(1), ils.Skip(1) }.SelectMany(s => s);      //排序操作,第二個原型可以加參數,比較器,二次排序用thenby,orderbydesding類似      var varOrderby = ils.OrderBy(p => p.IDCode.Length);      //reverse相反序列輸出      //Join和JoinGroup p119       IEnumerable<IGrouping<string,Employee>> items = ils.GroupBy(p => p.littleName);      IEnumerable<IGrouping<string,Department>> items1= ils.GroupBy(p => p.IDCode, q => q.Department);      //集合操作符 distinct,union(并集區別于Concat),intersect(連接后重複元素的序列),except(刪除參數中與自己重複的元素)      var ca = ils.Distinct();      List<Employee> ils1 = ils.Take(2).ToList<Employee>();      ils1.Add(new Employee() { IDCode = "我加的", Age = 33, littleName = "xixi" });      foreach (var v in ils.Except(ils1))      {        Console.WriteLine(v.littleName);      }      //元素操作符      var ilsDefaultIfEmpty = ils.Where(p => p.IDCode == "hehe").DefaultIfEmpty().First();      var ilsDefaultIfEmpty1 = ils.Where(p => p.IDCode == "hehe").DefaultIfEmpty(new Employee() { IDCode="heheid"}).First();      //生成操作符 Enumerable靜態方法Range,Repeat,      IEnumerable<int> EnumRange = Enumerable.Range(2, 20);      foreach (int i in EnumRange)      {        Console.WriteLine(i);      }      //p145            string str = string.Empty;      //cast,ofType,AsEnumerable()[將序列編程序列,適用于Linq To Sql]            #endregion