实体框架 - LINQ表达映射多对多

Question

我想找到一个User并为该User填充ICollection<Role>

我有用户

public class User {
   public string Id { get; set; }
   public string UserName { get; set; }
   public ICollection<Role> Roles { get; set; }
}

和角色

public class Role {
   public string Id {get; set; }
   public string Name { get; set; }
}

我的数据库看起来像这样

我想通过Id获得一个特定的用户，所有他的角色只有一个SQL调用。

_context是我的DbContext，我们可以在其中排队User，Roles和UserRoles

使用以下sql命令，我得到了我正在寻找的数据

from users in _context.Users
where users.Id == id
join userRoles in _context.UserRoles on users.Id equals userRoles.UserId
join roles in _context.Roles on userRoles.RoleId equals roles.Id
select new
{
    UserID = users.Id,
    UserName = users.UserName,
    RoleID = roles.Id,
    RoleName = roles.Name
};

我的问题

我想将此结果映射到User类，它应该创建一个用户和一个ICollection of Roles

我怎样才能做到这一点？

可以使用AutoMapper吗？ 怎么样？

提前致谢！ 亚历克斯

PS：我不想使用Identity提供的商店，因为有很多额外的信息要从数据库加载并控制对它的调用次数

Answer 1

试试以下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;
using System.Xml.Serialization;


namespace ConsoleApplication63
{
    class Program
    {

        static void Main(string[] args)
        {


            Context _context = new Context() {
                UserRoles = new List<UserRole>() {
                    new UserRole() { RoleId = "1", UserId = "1"},
                    new UserRole() { RoleId = "2", UserId = "3"},
                    new UserRole() { RoleId = "3", UserId = "2"},
                    new UserRole() { RoleId = "4", UserId = "4"}
                    },
                Users = new List<User>() {
                    new User() { 
                        Id = "3", UserName = "ABC", Roles = new List<Role> {
                            new Role() { Id = "100", Name = "ABC"},
                            new Role() { Id = "101", Name = "DEF"},
                            new Role() { Id = "102", Name = "GHI"},
                            new Role() { Id = "103", Name = "JKL"},
                            new Role() { Id = "104", Name = "MNO"}
                        }
                    }
                },
                Roles = new List<Role>() {
                    new Role() { Name = "XYZ", Id = "2"}
                }
            };


            string id = "3";
            List<UserRole> results = (from users in _context.UserRoles
                where users.UserId == id
                join  user in  _context.Users  on users.UserId equals user.Id
                join role in _context.Roles on users.RoleId  equals role.Id
                select   new  { Roles = user.Roles, UserId = user.Id})
                .Select(x => x.Roles.Select(y => new UserRole() { RoleId = y.Id, UserId = x.UserId}).ToList()).FirstOrDefault();
        }


    }
    public class Context
    {
        public List<User> Users { get; set; }
        public List<Role> Roles{ get; set; }
        public List<UserRole> UserRoles{ get; set; }
    }
    public class UserRole
    {
        public string UserId { get; set; }
        public string RoleId { get; set; }
    }
    public class User {
       public string Id { get; set; }
       public string UserName { get; set; }
       public List<Role> Roles { get; set; }
    }


    public class Role {
       public string Id {get; set; }
       public string Name { get; set; }
    }



}

Answer 2

我认为您需要使用GroupBy对结果进行分组，并对Roles集合使用适当的投影。 考虑到您的初始查询，您可以执行以下操作（我使用的是流畅的语法，您可以将其转换为查询语法）：

var initialQuery = from users in _context.Users
            where users.Id == id
            join userRoles in _context.UserRoles on users.Id equals userRoles.UserId
            join roles in _context.Roles on userRoles.RoleId equals roles.Id
            select new
            {
                UserID = users.Id,
                UserName = users.UserName,
                RoleID = roles.Id,
                RoleName = roles.Name
            };

IEnumerable<User> result = initialQuery
                .GroupBy(x => new { x.UserID, x.UserName })
                .Select(x => new User
                {
                    Id = x.Key.UserID,
                    UserName = x.Key.UserName,
                    Roles = x.Select(a => new Role { Id = a.RoleID, Name = a.RoleName }).ToList() as ICollection<Role>
                });