Linq lambda加入错误

Question

我一直在关注Pro ASP.net MVC 2框架，我发现它非常出色。但这是一个真正的学习曲线，现在我陷入困境。

在本书中，您将构建如下所示的内容，以便进行分页。

public ViewResult List([DefaultValue(0)] string cityzip, [DefaultValue(1)] int page) 
{ 

var roomsToShow = roomsRepository.Rooms.Where(x => x.CountryID == cityzip); 

var viewModel = new RoomsListViewModel 
{ 

    Rooms = roomsToShow.Skip((page - 1) * PageSize).Take(PageSize).ToList(), 
    PagingInfo = new PagingInfo 
    { 
     CurrentPage = page, 
     ItemsPerPage = PageSize, 
     TotalItems = roomsToShow.Count() 
    } 
}; 
return View(viewModel); // Passed to view as ViewData.Model (or simply Model) 

} 

我觉得需要去适应这一点，这样我就可以做搜索

public ViewResult List([DefaultValue(0)] string cityzip, [DefaultValue(1)] int page) 
{ 

var roomsToShow = roomsRepository.Rooms.Join(
        roomCoordinatesRepository.RoomCoordinates, 
        room => room.RoomID, 
        roomCoordinate => roomCoordinate.RoomID, 
        (room, roomCoordinate) => new { RoomCoordinate = roomCoordinate, Room = room }); 

var viewModel = new RoomsListViewModel 
{ 

    Rooms = roomsToShow.Skip((page - 1) * PageSize).Take(PageSize).ToList(), 
    PagingInfo = new PagingInfo 
    { 
     CurrentPage = page, 
     ItemsPerPage = PageSize, 
     TotalItems = roomsToShow.Count() 
    } 
}; 
return View(viewModel); // Passed to view as ViewData.Model (or simply Model) 

} 

一个加入...但我马上就得到一个智能感知错误说 - 无法隐式转换类型'System.Collections.Generic.List<AnonymousType#1>'到'System.Collections.Generic.IList<MeetingRoom.Domain.Entities.Room>'。一个明确的转换存在（你是否缺少演员？）

我明显不明白代码，足以找出错误。我也感觉有点出我的深度与此LAMDA LINQ东西

室是被定义为一个域对象：

namespace MeetingRoom.Domain.Entities 
    { 
     [Table(Name = "Rooms")] 
     public class Room 
     { 
      [Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert)] 
      public int RoomID { get; set; } 
      [Column] public string Name { get; set; } 
      [Column] public string Description { get; set; } 
      [Column] public decimal Price { get; set; } 
      [Column] public string Category { get; set; } 
      [Column] public string Pcode { get; set; } 
      [Column] public int CountryID { get; set; } 


      public MeetingRooms.Domain.entities.RoomCoordinate RoomCoordinate { get; set; } 
     } 
    } 

，并代表我的室的桌子上。我是否需要某种代表房间和坐标表之间联接的父实体？

的坐标实体看起来是这样的：

namespace MeetingRooms.Domain.entities 
{ 
    [Table(Name = "RoomCoordinate")] 
    public class RoomCoordinate 
    { 
     [Column(IsPrimaryKey = true, IsDbGenerated = true, AutoSync = AutoSync.OnInsert, Name = "ID")] 
     public int CoordID { get; set; } 
     [Column] 
     public int RoomID { get; set; } 
     [Column] 
     public string Coordinates { get; set; } 
     [Column] 
     public decimal Latitude { get; set; } 
     [Column] 
     public decimal Longitude { get; set; } 
    } 
} 

的RoomsListViewModel看起来像如下： 命名空间MeetingRoomsMVC.WebUI.Models { 公共类RoomsListViewModel { 公众的IList RoomsWithCoordinates {获得;组; } public PagingInfo PagingInfo {get;组; }
}}

Answer 1

这里的基础上，OP的进一步说明我的建议：

1）创建一个同时拥有Room和RoomCoordinates信息的集合类：

public class RoomWithCoordinates 
{ 
    public Room Room { get; set; } 
    public RoomCoordinates Coordinates { get; set; } 
} 

2）修改控制器动作如下：

public ViewResult List([DefaultValue(0)] string cityzip, [DefaultValue(1)] int page) 
{ 

var roomsToShow = roomsRepository.Rooms.Join(
        roomCoordinatesRepository.RoomCoordinates, 
        room => room.RoomID, 
        roomCoordinate => roomCoordinate.RoomID, 
        (room, roomCoordinate) => new RoomWithCoordinates{ Coordinates = roomCoordinate, Room = room }); 

var viewModel = new RoomsListViewModel 
{ 

    RoomsWithCoordinates = roomsToShow.Skip((page - 1) * PageSize).Take(PageSize).ToList(), 
    PagingInfo = new PagingInfo 
    { 
     CurrentPage = page, 
     ItemsPerPage = PageSize, 
     TotalItems = roomsToShow.Count() 
    } 
}; 
return View(viewModel); // Passed to view as ViewData.Model (or simply Model) 

} 

3）修改您的RoomsListViewModel类和您的视图以反映这些更改。

Answer 2

的问题是，在此代码

var roomsToShow = roomsRepository.Rooms.Join(
       roomCoordinatesRepository.RoomCoordinates, 
       room => room.RoomID, 
       roomCoordinate => roomCoordinate.RoomID, 
       (room, roomCoordinate) => new { RoomCoordinate = roomCoordinate, Room = room }); 

你就构造匿名类型对象的IEnumerable：(room, roomCoordinate) => new { RoomCoordinate = roomCoordinate, Room = room }

，然后在你的下一行”重新尝试将其分配到Room的列表中。

的问题可以通过最初创建正确的项目类型的IEnumerable解决：

var roomsToShow = roomsRepository.Rooms.Join(
       roomCoordinatesRepository.RoomCoordinates, 
       room => room.RoomID, 
       roomCoordinate => roomCoordinate.RoomID, 
       (room, roomCoordinate) => new MeetingRoom.Domain.Entities.Room{ RoomCoordinate = roomCoordinate, Room = room }); 

（注意在lambda类名）。