LINQ 语句

基本语法
var result = from item
in container
orderby value ascending/descending
select item;

1. 获取全部记录
   var allCars = from c in myCars select c;
   (提取指定行记录)
   var allCars = (from c in myCars select c).Take(5);//提取前 5 个数据
   (模糊查询)
   var quest = from qu in mdc.Question
   where qu.Question1.Contains(“数”)
   select qu;//模糊查询
   --------qu.Question1.Contains(“数”)//Linq 的表的哪列的 Contains()的方法
   (Linq 通过对象向数据库添加数据)
   NewsInfo newnf = new NewsInfo();
   newnf.newscontext = nf.newscontext;
   newnf.newsauthor = nf.newsauthor;
   newnf.newstime = DateTime.Now;//得到系统时间
   mdc.NewsInfo.InsertOnSubmit(newnf);//标记添加状态
   mdc.SubmitChanges();//执行添加
2. 只获取字段名称
   var names = from c in myCars select c.PetName;这里 names 就是隐式类型的变量。
3. 使用 Enumerable.Distinct()
   var makes = (from c in myCars select c.Make).Distinct();
4. 即可以在定义的时候调用 Enumberalbe 扩展函数
   var names = from c in myCars select c.PetName;
   foreach (var n in names)
   { Console.WriteLine(“Name: {0}”, n); } 也可以在兼容的数组类型上调用
   var makes = from c in myCars select c.Make;
   Console.WriteLine(“Distinct makes:”);
   foreach (var m in makes.Distinct())
   {
   Console.WriteLine(“Make: {0}”, m);
   }
   var onlyBMWs = from c in myCars
   where c.Make == “BMW” select c;
   var onlyFastBMWs = from c in myCars
   where c.Make == “BMW” && c.Speed >= 100 select c;
5. 生成新的数据类型（投影）
   var makesColors = from c in myCars select new {c.Make, c.Color};
6. Reverse()
   var subset = (from c in myCars select c).Reverse();
   foreach (Car c in subset)
   {
   Console.WriteLine(“{0} is going {1} MPH”, c.PetName, c.Speed);
   }
   或者
   var subset = from c in myCars select c;
   foreach (Car c in subset.Reverse())
   {
   Console.WriteLine(c.ToString());
   }
7. 排序
   默认是 ascending
   var subset = from c in myCars orderby c.PetName select c;
   subset = from c in myCars
   where c.Speed > 55 orderby c.PetName descending select c;
   默认顺序时也可以明确指明
   var subset = from c in myCars
   orderby c.PetName ascending select c; 8. Enumerable.Except()