如何构建这个LINQ表达式？

Question

我有一个类似这样的类：

class UserProfile { public int Id; public int? ParentId; public string Name; public string Role; }

IEnumerable<UserProfile> users = new List<UserProfile>{
        new UserProfile(){Id = 1, ParentId = null,  Name = "Admin1", Role = "Admin" },
        new UserProfile(){Id = 2, ParentId = 1,  Name = "User2", Role = "Admin" },
        new UserProfile(){Id = 3, ParentId = 1,  Name = "User3", Role = "Admin" },
        new UserProfile(){Id = 3, ParentId = null,  Name = "Admin2", Role = "Admin" },
        new UserProfile(){Id = 4, ParentId = 3,  Name = "User4", Role = "Admin" },
        new UserProfile(){Id = 5, ParentId = null,  Name = "User5", Role = "Admin" },
        new UserProfile(){Id = 6, ParentId = 3,  Name = "User6", Role = "Admin" },
    };  

null

var adminsOnly = users.Where(p => p.Role.Equals("Admin")).OrderBy(p => p.Id);
var usersOnly = users.Where(p => p.Role.Equals("User")).OrderBy(p => p.Id);

多谢.

注意：可以有没有管理员的用户，也可以有没有用户的管理员。

Answer 1

试试这个：

users.Where(x => x.Role == "User" && x.ParentID == null)
     .Concat(users.Where(x => x.Role == "Admin")
                  .ToDictionary(x => x, 
                                x => users.Where(u => u.ParentId == x.Id));
                  .SelectMany(x => new[] {x.Key}.Concat(x.Value)));

这将为您提供一个IEnumerable ，所有用户都列在他们的admin之后，所有没有admin的用户都列在第一位。