更新c項目列表＃

Question

我想知道你是否可以建議我一種有效的方式來更新c＃中的項目列表。這是一個普通的例子：

如果CurrentList是

[ {Id: 154, Name: "George", Salary: 10 000} 
    {Id: 233, Name: "Alice", Salary: 10 000}] 

而且NewList是

[ {Id: 154, Name: "George", Salary: 25 000} 
    {Id: 234, Name: "Bob", Salary: 10 000}] 

那麼結果應該是：

[{Id: 154, Name: "George", Salary: 25 000} 
{Id: 234, Name: "Bob", Salary: 10 000} ] 

我不想只是爲了清除第一個並使用第二個值，但想要更新具有相同ID的值，刪除那些值已被刪除並添加任何新的。

在此先感謝。

Answer 1

我會做這樣的事情：（用於ordinairy列表）

// the current list 
var currentList = new List<Employee>(); 
currentList.Add(new Employee { Id = 154, Name = "George", Salary = 10000 }); 
currentList.Add(new Employee { Id = 233, Name = "Alice", Salary = 10000 }); 

// new list 
var newList = new List<Employee>(); 
newList.Add(new Employee { Id = 154, Name = "George", Salary = 25000 }); 
newList.Add(new Employee { Id = 234, Name = "Bob", Salary = 10000 }); 

// clean up 
foreach (var oldEmployee in currentList.ToArray()) 
    if (!newList.Any(item => oldEmployee.Id == item.Id)) 
     currentList.Remove(oldEmployee); 

// check if the new item is found within the currentlist. 
// If so? update it's values else add the object. 
foreach (var newEmployee in newList) 
{ 
    var oldEmployee = currentList.FirstOrDefault(item => item.Id == newEmployee.Id); 
    if (oldEmployee == null) 
    { 
     // add 
     currentList.Add(newEmployee); 
    } 
    else 
    { 
     // modify 
     oldEmployee.Name = newEmployee.Name; 
     oldEmployee.Salary = newEmployee.Salary; 
    } 
} 

---

可以加速這一過程，使用字典，但（現在）這不是你的問題

Answer 2

你可以

 for (int i = 0; i < NewList.Count; i++) 
     { 
      var record = CurrentList.FirstOrDefault(item => item.Id == NewList[i].Id); 
      if (record == null) { CurrentList.Add(NewList[i]); } 
      else { record.Id = NewList[i].Id; record.Name = NewList[i].Name; record.Salary = NewList[i].Salary; } 
     } 

     CurrentList.RemoveAll(item => NewList.FirstOrDefault(item2 => item2.Id == item.Id) == null); 

使用示例：：與使用的for循環和LINQ表達做 Example

Answer 3

如果'Id'位於某種類型的接口上，則LINQ'y包裝在擴展方法中的版本可以修改爲通用。

合併操作可能是實體對象（如員工）上的Merge（）方法，但我選擇在此處使用委託。

public class Tests 
{ 
    [Test] 
    public void MergeSpike() 
    { 
     // the current list 
     var currentList = new List<Employee>(); 
     currentList.Add(new Employee { Id = 154, Name = "George", Salary = 10000 }); 
     currentList.Add(new Employee { Id = 233, Name = "Alice", Salary = 10000 }); 

     // new list 
     var newList = new List<Employee>(); 
     newList.Add(new Employee { Id = 154, Name = "George", Salary = 25000 }); 
     newList.Add(new Employee { Id = 234, Name = "Bob", Salary = 30000 }); 

     currentList.Merge(newList, (o, n) => 
     { 
      if(o.Id != n.Id) throw new ArgumentOutOfRangeException("Attempt to merge on mismatched IDs"); 
      o.Name = n.Name; 
      o.Salary = n.Salary; 
     }); 


     Assert.That(currentList.Count(), Is.EqualTo(2)); 
     Assert.That(currentList.First(c => c.Id == 154).Salary, Is.EqualTo(25000)); 
     Assert.That(currentList.Any(c => c.Id == 233), Is.False); 
     Assert.That(currentList.First(c => c.Id == 234).Salary, Is.EqualTo(30000)); 


    } 
} 

public class Employee 
{ 
    public int Id { get; set; } 
    public string Name { get; set; } 
    public int Salary { get; set; } 
} 

public static class EmployeeListExtensions 
{ 
    public static void Merge(this List<Employee> currentList, IEnumerable<Employee> newList, Action<Employee, Employee> merge) 
    { 
     // Updates 
     currentList.Where(e => newList.Any(n => n.Id == e.Id)) 
      .ToList().ForEach(e => merge(e, newList.First(n1 => n1.Id == e.Id))); 

     // Deletes 
     var remove = currentList.Where(cl => newList.All(nl => cl.Id != nl.Id)).ToList(); 
     currentList.RemoveAll(e => remove.Any(r => r.Id == e.Id)); 

     // Inserts 
     currentList.AddRange(newList.Where(nl => currentList.Any(c => c.Id != nl.Id))); 
    } 
}