LINQ to SQL查询

Question

我有一个LINQ to SQL查询来检索所有用户与他们的角色一起：

var userRoles = from u in db.GetTable<User>() 
          join ur in db.GetTable<UserRole>() 
           on u.UserID equals ur.UserID 
          join r in db.GetTable<Role>() 
           on ur.RoleID equals r.RoleID 
           orderby u.UserID 
          select new 
             { 
              u.UserID, 
              r.RoleName 
             }; 

在系统中的用户可以拥有多个角色。这个查询（以表格形式）的结果是这样的：

1管理员
1员工
2员工
3员工

我怎样才能重新写这个查询返回的所有用户角色等逗号分隔值：

1联系，员工
2雇员
3雇员

Answer 1

嘿库马尔，我创建了一个小型控制台应用程序来模仿我相信你有的数据。我认为它展现了你正在寻找的行为。这不是世界上最伟大的代码，但我认为算法是关键。我只是将ToString（）的一个快速覆盖放在一起以正确显示数据。

我做的最主要的变化是创建一个定义的类要显示的数据，并打破LINQ查询分成两个独立的部分：

using System; 
using System.Collections.Generic; 
using System.Linq; 

namespace Test 
{ 
    class Program 
    { 
     static void Main() 
     { 
      var users = new List<User> 
          { 
           new User 
            { 
             UserID = "1" 
            }, 
           new User 
            { 
             UserID = "2" 
            }, 
           new User 
            { 
             UserID = "3" 
            } 
          }; 

      var roles = new List<Role> 
          { 
           new Role 
            { 
             RoleID = "1", 
             RoleName = "Admin" 
            }, 
           new Role 
            { 
             RoleID = "2", 
             RoleName = "Employee" 
            } 
          }; 

      var userRoles = new List<UserRole> 
           { 
            new UserRole 
             { 
              UserID = "1", 
              RoleID = "1" 
             }, 

            new UserRole 
             { 
              UserID = "1", 
              RoleID = "2" 
             }, 

            new UserRole 
             { 
              UserID = "2", 
              RoleID = "2" 
             }, 

            new UserRole 
             { 
              UserID = "3", 
              RoleID = "2" 
             } 
           }; 

      var userRoles2 = from u in users 
          orderby u.UserID 
          select new UserList 
          { 
           UserID = u.UserID, 
           Roles = (from r in roles 
              join ur in userRoles 
              on u.UserID equals ur.UserID 
              where ur.RoleID == r.RoleID 
              select r).ToList() 
          }; 

      foreach (var item in userRoles2) 
      { 
       Console.WriteLine(item); 
      } 
      Console.ReadKey(); 
     } 
    } 

    public class User 
    { 
     public string UserID; 
    } 

    public class UserRole 
    { 
     public string UserID; 
     public string RoleID; 
    } 

    public class Role 
    { 
     public string RoleID; 
     public string RoleName; 
    } 

    public class UserList 
    { 
     public string UserID; 
     public List<Role> Roles; 

     public override string ToString() 
     { 
      string output = UserID + " "; 
      foreach (var role in Roles) 
      { 
       output += role.RoleName + ", "; 
      } 
      output = output.Substring(0, output.Length - 2); 
      return output; 
     } 
    } 
} 

Answer 2

这是做它的一种方式，没有测试它：

from u in db.GetTable<User>() 
         join ur in db.GetTable<UserRole>() 
          on u.UserID equals ur.UserID 
         join r in db.GetTable<Role>() 
          on ur.RoleID equals r.RoleID 
         orderby u.UserID 
         group u by u.UserID into g  
         select new 
           { 
            UserId = g.Key, 
            Roles = String.Join (" ,", g.UserRoles.SelectMany(c => c.Roles).Select(p=> p.RoleName).ToArray())) 
           };