asp.net從FindAll或Where修改列表而不修改搜索到的原始列表

Question

我試圖從findall或where創建一個新列表，並修改該新列表而不更改原始列表。從FindAll創建list2並對list2進行更改時，它不應該影響list1。怎麼來的？

編輯...兩個似乎工作的答案組合使用。任何預見的問題？編輯的工作代碼 編輯...它不工作。一個屬於對象屬性的類沒有複製其數據...任何想法？我看不出爲什麼複製或克隆對列表來說不簡單和簡單。

class Program 
{ 
    static void Main(string[] args) 
    { 
     Console.WriteLine("Started"); 
     List<SampleData> list1 = SampleData.MakeList(3); 
     for (int i = 0; i < list1.Count; i++) 
     { 
      Console.WriteLine("list1.Number => " + list1[i].Number); 
      Console.WriteLine("list1.Person => " + list1[i].Person); 
     } 
     List<SampleData> list2 = new List<SampleData>(list1.FindAll(m => m.Number == 1).Select(x => new SampleData().ShallowCopy())).ToList(); 
     for (int i = 0; i < list2.Count; i++) 
     { 
      list2[i].Person = "Person " + list2[i].Number; 
      Console.WriteLine("list2.Number => " + list2[i].Number); 
      Console.WriteLine("list2.Person => " + list2[i].Person); 
     } 

     SampleData sd = list2.Find(s => s.Number == 1); 
     Console.WriteLine("Apartment Number" + sd.apartment.BuildingLetter); // <<<<------------------- THROWING NULL EXCEPTION FOR APARTMENT 

     Console.WriteLine("-------AFTER MODIFYING NEW LIST----LIST1.Person SHOULD BE NULL---"); 
     for (int i = 0; i < list1.Count; i++) 
     { 
      Console.WriteLine("--list1.Number => " + list1[i].Number); 
      Console.WriteLine("--list1.Person => " + list1[i].Person); 
     } 
     for (int i = 0; i < list2.Count; i++) 
     { 
      Console.WriteLine("--list2.Number => " + list2[i].Number); 
      Console.WriteLine("--list2.Person => " + list2[i].Person); 
     } 
     Console.ReadLine(); 
     System.Environment.Exit(0); 
    } 

} 
class SampleData 
{  
    public int Number { get; set; } 
    public String Person { get; set; } 
    public Apartment apartment { get; set; } 
    public static List<SampleData> MakeList(int count) 
    { 
     List<SampleData> l = new List<SampleData>(); 
     for (int i = 0; i < count; i++) 
     { 
      SampleData d = new SampleData(); 
      d.apartment = new Apartment { RoomNumber = i, BuildingLetter = "letter-" + i }; 
      d.Number = i; 
      l.Add(d); 
     } 
     return l; 
    } 
    public SampleData ShallowCopy() 
    { 
     return (SampleData)this.MemberwiseClone(); 
    } 

} 
class Apartment 
{ 
    public int RoomNumber { get; set; } 
    public String BuildingLetter { get; set; } 
} 

Answer 1

您可以使用。 AsNoTracking（）的情況下，方法實體查詢惠蔭選擇從的DbContext或的ObjectContext

List<SampleData> list2 = new List<SampleData>(list1.Where(m => m.Number == 1).AsNoTracking().ToList()); 

---

，或者使用複製承包商像

class SampleData 
{ 
    public int Number { get; set; } 
    public String Person { get; set; } 

    public SampleData(SampleData obj) 
    { 
     This.Number=obj.Number; 
     This.Person=obj.Person; 
     .. 
     .. 
    } 
    public static List<SampleData> MakeList(int count) 
    { 
     List<SampleData> l = new List<SampleData>(); 
     for (int i = 0; i < count; i++) 
     { 
      SampleData d = new SampleData(); 
      d.Number = i; 
      l.Add(d); 
     } 
     return l; 
    } 
} 

然後

List<SampleData> list2 = new List<SampleData>(list1.Where(m => m.Number == 1).Select(x=>new SampleData(x)).ToList()); 

Answer 2

ShallowCopy是你的朋友。

像這樣在你的SampleData類中定義一個ShallowCopy（）方法。

class SampleData 
{ 
    public int Number { get; set; } 
    public String Person { get; set; } 
    public static List<SampleData> MakeList(int count) 
    { 
     List<SampleData> l = new List<SampleData>(); 
     for (int i = 0; i < count; i++) 
     { 
      SampleData d = new SampleData(); 
      d.Number = i; 
      l.Add(d); 
     } 
     return l; 
    } 

    public SampleData ShallowCopy() 
    { 
     return (SampleData)this.MemberwiseClone(); 
    } 

} 

然後填充列表2如下...

List<SampleData> list2 = new List<SampleData>(); 
foreach (SampleData sd in list1.Where(m => m.Number == 1)) 
{ 
    list2.Add(sd.ShallowCopy()); 
}