使用LINQ仅基于单个对象属性来获取两个对象列表之间的差异

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问题描述

狗类具有两个属性(名称和颜色)

the dog class has two properties (name and color)

假设我有两个IEnumerable列表:

Let's say I have two IEnumerable lists:

List1 [{name="Sam", color="Fawn"}, {name="Mary", color=""}, {name="Bob", color=""}]
List2 [{name="Mary", color="Black"},{name="Bob", color="Yellow"}]

我想获取只名称不同的狗对象列表

I want to get a list of dog objects that differ ONLY in name

所以我的退货清单看起来像

so my return list would look like

ListReturn: [{name="Sam", color="Fawn"}]

有道理吗?

我想用linq做到这一点.这是我尝试过的方法，但是没有用有帮助吗?

I want to do this with linq. This is what I've tried... and it's not workingany help?

  var missing = from l1 in List1
                join l2 in List2 on l1.Name equals l2.Name into merged
                from missed in merged.DefaultIfEmpty()
                select missed;

我可能是个傻瓜，但我整天盯着它看，无法理解.任何帮助将不胜感激.

I may be a complete moron, but I've stared at this all day and can't get it. any help would be appreciated.

推荐答案

从功能上讲，您拥有的是Except，但您不想使用整个项目的相等性，而是希望使用选定的属性作为钥匙.虽然可以为Except提供仅用于比较名称的自定义IEqualityComparer，但是编写比较器是相当容易出错的样板代码.我们可以编写一种相当容易地在投影键上执行Except的方法:

What you have is functionally Except, but instead of using equality of the whole item, you want to perform the Except using a selected property as the key. While you could provide a custom IEqualityComparer to Except that only compared names, writing that comparer is a fair bit of error prone boilerplate code. We can write a method that performs an Except on a projected key fairly easily:

public static IEnumerable<TSource> ExceptBy<TSource, TKey>(
    this IEnumerable<TSource> source,
    IEnumerable<TSource> other,
    Func<TSource, TKey> keySelector)
{
    var set = new HashSet<TKey>(other.Select(keySelector));
    foreach(var item in source)
        if(set.Add(keySelector(item)))
            yield return item;
}

这将执行除使用给定键而不是自定义相等比较器的操作.

This performs an except using the given key, instead of a custom equality comparer.

现在您的查询很简单:

var query = list1.ExceptBy(list2, dog => dog.name);

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EXCEPT