"Linq to object"实现以及错误排除

[starrycheng]

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.cs 59 62 Mycems.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.cs 60 91 Mycems.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;

}

[starrycheng]

完整的代码是这样的么：

1、实体类

namespace ServicesEntity
{
public class RoomLayerBuilding : INotifyPropertyChanged, IEqualityComparer<RoomLayerBuilding>
{
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"));
}
}


public bool Equals(RoomLayerBuilding x, RoomLayerBuilding y)
{
return (x.BuildingNo.Trim() == y.BuildingNo.Trim() && x.BuildingName.Trim() == y.BuildingName.Trim());
}

public int GetHashCode(RoomLayerBuilding obj)
{
return obj.BuildingNo.GetHashCode() ^ obj.BuildingName.GetHashCode();
}




#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion

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

}
}


Enumerable<RoomLayerBuilding> roomlayerbuildings = this.GetRoomLayerBuildingDatas().Distinct(new RoomLayerBuilding());

foreach (var item in roomlayerbuildings)
{
ListMenuCatalog lmc = new ListMenuCatalog();
lmc.CatalogName = item;

}
return listmenucatalogs;

2、处理数据集

Enumerable<RoomLayerBuilding> roomlayerbuildings = this.GetRoomLayerBuildingDatas().Distinct(new RoomLayerBuilding());

foreach (var item in roomlayerbuildings)
{
ListMenuCatalog lmc = new ListMenuCatalog();
lmc.CatalogName = item;

}
return listmenucatalogs;

问题一：“ Enumerable<RoomLayerBuilding> ”这一个提示错误，信息如下：

错误
1 非泛型 类型“System.Linq.Enumerable”不能与类型实参一起使用
C:\Users\Administrator\Desktop\DX4.0\Mycems.BLL\RoomLayerBuildingDatas.cs
65 13
Mycems.BLL

问题二：实体类“RoomLayerBuilding”直接继承“IEqualityComparer<RoomLayerBuilding>”，这个可以么？ 还需不需要重新创建一个“RoomLayerBuildingComparer”类？？？

问题三：“var roomlayerbuildings = this.GetRoomLayerBuildingDatas().Select(rlb => rlb.BuildingNo).Distinct().ToList();”这样可以筛选数据么？

var roomlayerbuildings = this.GetRoomLayerBuildingDatas().Select(rlb => rlb.BuildingNo).Distinct().ToList();

foreach (var item in roomlayerbuildings)
{
ListMenuCatalog lmc = new ListMenuCatalog();
lmc.CatalogName = item.BuildingName;

}

问题：提示“string”不包含"BuildingName"的定义，为什么？？？

错误信息如下：
错误 1 “string”不包含“BuildingName”的定义，并且找不到可接受类型为“string”的第一个参数的扩展方法“BuildingName”(是否缺少 using 指令或程序集引用?) C:\Users\Administrator\Desktop\DX4.0\Mycems.BLL\RoomLayerBuildingDatas.cs 66 40 Mycems.BLL

[q107770540]

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：

  var listbybuilding = roomlayerbuildings.GroupBy(r => r.BuildingNo).Select(g=>g.First()).ToList();  

[q107770540]

//问题2
var 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");

[starrycheng]

[Quote=引用 3 楼 的回复:]

C# code


//问题2
var 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……
[/Quote]

顶一下。。。

[starrycheng]

[Quote=引用 3 楼 的回复:]

C# code


//问题2
var 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……
[/Quote]

敢问大侠，有关于“Linq to object”、“Linq to SQL”、“Linq to EF”、“Linq to DataSet”的资料没？？？

主要是要熟悉“语法和函数”，谢谢了。。。

[q107770540]

http://topic.csdn.net/u/20101111/09/ea049af5-d079-4a13-8c1d-e1a3350a830d.html

[starrycheng]

[Quote=引用 6 楼 的回复:]

http://topic.csdn.net/u/20101111/09/ea049af5-d079-4a13-8c1d-e1a3350a830d.html
[/Quote]

3KS

[starrycheng]

要写一篇博客总结下“Linq”的使用了啊。。。