MVC ---- Linq查询

Linq查询：编译后，会生成对应的标准查询运算符！所以说，Linq只是类似与Sql的一种更加友好的语法而已；

 

public class LinqDemo{
    
    public static void TestTen(){
        List<User> usList =Five.GetUserList();
        List<Dept> dtLsit =Five.GetDeptList();
        
        //1. 从老集合中查询每一个元素存入新集合
        //取数据到新的集合中
        var newUserList = from u in usList select u;
        
        //2. Where条件  &&表示and
        var newDtList = from d in dtLsit where d.DeptId= '0001' && d.PepName==10 select d;
        
        //3. Orderby
        var newDtList = from d in dtLsit where d.DeptId= '0001' && d.PepName==10 orderby d.DeptId orderby d.PepNum descending select d;
        
        //4. Join关联数据
        var joinResult = from u in usList join d in dtLsit on u.DeptId equals d.DeptId select new {UserName=u.Name,LoginName=u.LoginName,Deptname=d.DeptName};
        //遍历
        foreach(var item in joinResult){
            Console.WriteLine(item.DeptName);
        }
        
        
        //5. Group By 分组查询
        var groupList = from u in usList group u by u.DeptId;
        //遍历
        foreach(var group in groupList){
            Console.WriteLine(group.Key);
            foreach(var item in group){
                Console.WriteLine(item.Tostring());
            }
        }
    }
}