Linq在查询中添加项目到列表答案

【问题标题】：Linq adding items to list in the queryLinq在查询中添加项目到列表
【发布时间】：2022-10-12 21:18:27
【问题描述】：

再会，我有一个问题。我有三个域对象

 public class User
{
    public Guid Id { get; set; }
    public string Username { get; set; }
    public string EmailAddress { get; set; }
    public string Password { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    [NotMapped]
    public List<string> Roles { get; set; }

    //nav prop
    public List<User_Role> UserRoles { get; set; }
}

 public class User_Role
{
    public Guid Id { get; set; }

    public Guid UserId { get; set; }
    //nav prop
    public User User { get; set; }

    public Guid RoleId { get; set; }
    //nav prop
    public Role Role { get; set; }
}
 public class Role
{
    public Guid Id { get; set; }
    public string Name { get; set; }

    public List<User_Role> UserRoles { get; set; }
}

我想从他们创建 DTO 对象

 public class ReturnUserDto
{
    public Guid Id { get; set; }
    public string Username { get; set; }
    public string EmailAddress { get; set; }
    public string Password { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public List<string> Roles { get; set; }
}

我为它创建了一个控制器

[Route("api/[controller]")]
[ApiController]
public class UserController : ControllerBase
{
    public readonly IUserRepository _userRepository;
    public readonly IRoleRepository _roleRepository;
    public readonly IUserRoleRepository _userRoleRepository

    public UserController(IUserRepository userRepository, IRoleRepository IRoleRepository,
        IUserRoleRepository userRoleRepository)
    {
        _userRepository = userRepository;
        _roleRepository = IRoleRepository;
        _userRoleRepository = userRoleRepository;   
    }

    [HttpGet]
    public async Task<IActionResult> GetAllUsersAsync()
    {
        var users = _userRepository.GetAllAsync();

        var usersDto = users.ConvertToDto(unknow arguments)


    }
}

我正在尝试通过使用静态 DtoConverstion 函数来实现它看起来像这样

public static IEnumerable<ReturnUserDto> ConvertToDto(this IEnumerable<User> users,
        IEnumerable<Role>  Role)
    {
        var  returnUserDto = (from user in users
                              select new ReturnUserDto
                              {
                                  Id = user.Id,
                                  Username = user.Username,
                                  EmailAddress = user.EmailAddress,
                                  Password = user.Password,
                                  FirstName = user.FirstName,
                                  LastName = user.LastName,
                                  Roles = ?(Something like Role.name)
                              })
    }

我如何实现它？我知道我需要使用 user_roles 从中获取特定用户的角色，然后将其添加到 DtoConvertion 函数。我只是不知道该怎么做。

【问题讨论】：

标签： linq dto

【解决方案1】：

可以通过多种方式进行

传入用户角色的值，并在转换方法中使用它来处理

    ...
    var users = _userRepository.GetAllAsync();
    var userRoles = _userRoleRepository.GetAllAsync();

    var usersDto = users.ConvertToDto(userRoles)
    ...


    public static IEnumerable<ReturnUserDto> ConvertToDto(this IEnumerable<User> users,
        IEnumerable<UserRole> userRoles)
    {
        var  returnUserDto = (from user in users
                              select new ReturnUserDto
                              {
                                  Id = user.Id,
                                  Username = user.Username,
                                  EmailAddress = user.EmailAddress,
                                  Password = user.Password,
                                  FirstName = user.FirstName,
                                  LastName = user.LastName,
                                  Roles = userRoles.Where(s => s.UserId == user.Id).ToList
                              })
    }

在 EF 中使用 Include() 方法方法来获取 UserRole 的值以及用户，同时获取并将其转换为 DTO。与第一种方法相比，这只需要一次数据库调用。

【讨论】：