Linq lambda加入錯誤

Question

我一直在關注Pro ASP.net MVC 2框架，我發現它非常出色。但這是一個真正的學習曲線，現在我陷入困境。

在本書中，您將構建如下所示的內容，以便進行分頁。

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) 

} 

我覺得需要去適應這一點，這樣我就可以做搜索

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) 

} 

一個加入...但我馬上就得到一個智能感知錯誤說 - 無法隱式轉換類型'System.Collections.Generic.List<AnonymousType#1>'到'System.Collections.Generic.IList<MeetingRoom.Domain.Entities.Room>'。一個明確的轉換存在（你是否缺少演員？）

我明顯不明白代碼，足以找出錯誤。我也感覺有點出我的深度與此LAMDA LINQ東西

室是被定義爲一個域對象：

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; } 
     } 
    } 

，並代表我的室的桌子上。我是否需要某種代表房間和座標表之間聯接的父實體？

的座標實體看起來是這樣的：

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看起來像如下： 命名空間MeetingRoomsMVC.WebUI.Models { 公共類RoomsListViewModel { 公衆的IList RoomsWithCoordinates {獲得;組; } public PagingInfo PagingInfo {get;組; }
}}

Answer 1

這裏的基礎上，OP的進一步說明我的建議：

1）創建一個同時擁有Room和RoomCoordinates信息的集合類：

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

2）修改控制器動作如下：

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類和您的視圖以反映這些更改。

Answer 2

的問題是，在此代碼

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

你就構造匿名類型對象的IEnumerable：(room, roomCoordinate) => new { RoomCoordinate = roomCoordinate, Room = room }

，然後在你的下一行」重新嘗試將其分配到Room的列表中。

的問題可以通過最初創建正確的項目類型的IEnumerable解決：

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類名）。