Linq:在进行投影时设置属性 [英] Linq: set a property while doing a projection

问题描述

我正在做一个使用First元素的简单GroupBy，但是我想修改每个结果的一个属性.

I'm doing a simple GroupBy taking the First element but I want to modify one of the property of each result.

class M
{
 public string Name {get; set;}
 public int NOfPeopleWithTheSameName {get; set;}
 public string P1 {get; set;}
 public string P2 {get; set;}
 public string P3 {get; set;}
 public string P4 {get; set;}
 public string P5 {get; set;}
}  


List<M> myList = GetMyList();


var l2 = myList
   .GroupBy(m => m.Name)
   .Select(group => new M { Name = group.Key, NOfPeopleWithTheSameName = group.Count() });

这很简单，但是如果类具有许多属性(因为每个属性值都应复制到新属性)，则这种方法不是最佳方法吗?我应该一一复制.

This is pretty easy, but this way is not the best if the class has many properties (since every property value should be copied to the new one)? I should copy them one by one.

我只想简单地获取元素并更改属性NOfPeopleWithTheSameName

I would like to simply take the element and change the property NOfPeopleWithTheSameName

推荐答案

您无需创建新的M，您可以返回现有的M，例如:

You don't need to create a new M, you can return the existing one, for example:

var l2 = myList
   .GroupBy(m => m.Name)
   .Select(group => 
   {
        var m = group.First();
        m.NOfPeopleWithTheSameName = group.Count();
        return m;
   });

但是，如果您只是为此目的在模型中添加属性，我建议您改用另一个类包装初始模型和计数-不要污染您的模型.例如，您可能有一个像这样的通用包装器类:

However, if you are going to add a property to your model just for this, I would suggest instead having a different class that wraps the initial model and the count - don't pollute your models. For example, you could have a generic wrapper class like this:

public class ModelCount<T>
{
    public T Model { get; set; }
    public int Count { get; set; }
}

现在像这样分组:

var l2 = myList
   .GroupBy(m => m.Name)
   .Select(group => new ModelCount<M> 
   {
        Model = group.First(),
        Count = group.Count()
   });

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