"Linq to object"实现以及异常排除

"Linq to object"实现以及错误排除
首先感谢“q107770540”等网友的帮助。

一、"Linq to object"方法实现
public List<ListMenuCatalog> GetRoomLayerBuildingLists()
  {
  List<ListMenuCatalog> listmenucatalogs = new List<ListMenuCatalog>();
  List<RoomLayerBuilding> roomlayerbuildings = this.GetRoomLayerBuildingDatas();
  //var listbybuilding = roomlayerbuildings.Distinct(r => r.BuildingNo).ToList(); 
  [color=#FF0000]问题一：“roomlayerbuildings.Distinct(r => r.BuildingNo).ToList()”这样不对么，为什么会出现这样的错误，信息如下？
   
  错误1无法将 lambda 表达式 转换为类型“System.Collections.Generic.IEqualityComparer<ServicesEntity.RoomLayerBuilding>”，因为它不是委托类型C:\Users\Administrator\Desktop\DX4.0\Mycems.BLL\RoomLayerBuildingDatas.cs5962Mycems.BLL

   
[/color]

  //var listbybuilding = (from lb in roomlayerbuildings select roomlayerbuildings.BuildingNo).Distinct();
问题二：“from lb in roomlayerbuildings select roomlayerbuildings.BuildingNo).Distinct()”这样写不对么？ 为什么会出现这样的错误，信息如下？

错误1“System.Collections.Generic.List<ServicesEntity.RoomLayerBuilding>”不包含“BuildingNo”的定义，并且找不到可接受类型为“System.Collections.Generic.List<ServicesEntity.RoomLayerBuilding>”的第一个参数的扩展方法“BuildingNo”(是否缺少 using 指令或程序集引用?)C:\Users\Administrator\Desktop\DX4.0\Mycems.BLL\RoomLayerBuildingDatas.cs6091Mycems.BLL



  return listmenucatalogs;
  }


问题三：如果从“roomlayerbuildings”集合中筛选出“DpRoomNo”、“RoomName”两个属性字段不重复的的结果集，应该怎样写？


  问题四：“var query3=room.Where(r=>r.DpRoomNo=="001").ToList();”返回的是一个“List”，要获取其中的值，还要将“Var query3”转化为“List”集合，然后获取第一个是么？还有其它好的方法么？



完整实体类：
public class RoomLayerBuilding : INotifyPropertyChanged
  {
  public RoomLayerBuilding() { }


   

  /// <summary>
  /// 房间编号
  /// </summary>
  public String DpRoomNo
  {
  get
  {
  return _dproomno;
  }
  set
  {
  _dproomno = value;
  if (PropertyChanged != null)
  PropertyChanged(this, new PropertyChangedEventArgs("DpRoomNo"));
  }
  }


  /// <summary>
  /// 房间名称
  /// </summary>
  public String RoomName
  {
  get
  {
  return _dproomname;
  }
  set
  {
  _dproomname = value;
  if (PropertyChanged != null)
  PropertyChanged(this, new PropertyChangedEventArgs("RoomName"));
  }
  }


  /// <summary>
  /// 楼层编号
  /// </summary>
  public String LayerNo
  {
  get
  {
  return _dplayerno;
  }
  set
  {
  _dplayerno = value;
  if (PropertyChanged != null)
  PropertyChanged(this, new PropertyChangedEventArgs("LayerNo"));
  }
  }


  /// <summary>
  /// 建筑编号
  /// </summary>
  public String BuildingNo

  {
  get
  {
  return _dpbuildingno;
  }
  set
  {
  _dpbuildingno = value;
  if (PropertyChanged != null)
  PropertyChanged(this, new PropertyChangedEventArgs("BuildingNo"));
  }
  }


  /// <summary>
  /// 建筑名称
  /// </summary>
  public String BuildingName
  {
  get
  {
  return _dpbuildingname;
  }
  set
  {
  _dpbuildingname = value;
  if (PropertyChanged != null)
  PropertyChanged(this, new PropertyChangedEventArgs("BuildingName"));
  }
  }

   

   

   

  #region INotifyPropertyChanged Members
  public event PropertyChangedEventHandler PropertyChanged;
  #endregion

  String _dproomno;
  String _dproomname;
  String _dplayerno;
  String _dpbuildingno;
  String _dpbuildingname;
   
  }

[解决办法]
1.vroomlayerbuildings.Distinct(r => r.BuildingNo).ToList();
返回的是由BuildingNo值组成的int数组（BuildingNo类型是int）
你如果想返回ListMenuCatalog类型的数组，可以这样：

C# code

  var listbybuilding = roomlayerbuildings.GroupBy(r => r.BuildingNo).Select(g=>g.First()).ToList();
[解决办法]
C# code
//问题2var listbybuilding = (from lb in roomlayerbuildings select lb.BuildingNo).Distinct();//其实等价于：var listbybuilding = roomlayerbuildings.Select(lb=> lb.BuildingNo).Distinct();问题3： 参考 http://blog.csdn.net/q107770540/article/details/5784646问题4： 如果只想获取第一个，可以这样：var query3=room.FirstOrDefault(r=>r.DpRoomNo=="001");
[解决办法]
http://topic.csdn.net/u/20101111/09/ea049af5-d079-4a13-8c1d-e1a3350a830d.html