Question

我一直在关注Pro ASP.net MVC 2 Framework这本书，我发现它非常精彩。但这是一个真正的学习曲线，现在我被卡住了。

在本书中，您构建了类似下面的内容，允许分页。

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) 

}

我认为需要对此进行调整，以便我可以在搜索中加入

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) 

}

...但是我立刻得到了一个智能错误说 - 无法隐式将'System.Collections.Generic.List<AnonymousType#1>'类型转换为'System.Collections.Generic.IList<MeetingRoom.Domain.Entities.Room>'。存在显式转换（您是否错过了演员？）

我显然不能很好地理解代码以找出问题所在。我也觉得这个lamda linq的东西有点超出我的深度

Room是一个域对象，定义为：

   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Room表。我是否需要某种代表房间和房间坐标表之间连接的父实体？

坐标实体看起来像这样：

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; }  
    }
}

RoomsListViewModel如下所示：名称空间MeetingRoomsMVC.WebUI.Models { 公共类RoomsListViewModel { 公共IList RoomsWithCoordinates {get;组; } public PagingInfo PagingInfo {get;组; }
} }

Answer 1

问题在于此代码

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

您正在构建IEnumerable个匿名类型的对象：(room, roomCoordinate) => new { RoomCoordinate = roomCoordinate, Room = room }

然后，在下一行中，您尝试将其分配到Room列表。

可以通过最初创建正确项目类型的IEnumerable来解决问题：

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lambda中的类名）。

Answer 2

以下是基于OP进一步描述的建议：

1）创建一个包含Room和RoomCoordinates信息的聚合类：

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

2）按如下方式修改您的控制器操作：

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课程和您的观点，以反映这些变化。

Linq lambda加入错误

2 个答案: