IEqualityComparer上的奇怪行为

本文关键字：IEqualityComparer | 更新日期: 2023-09-27 18:31:55

我正在尝试为我的对象实现一个IEqualityComparer，它基本上可以检测一个对象是否比另一个对象旧。以下更简单的示例将综合我想要完成的任务：

class Program
{
    static void Main(string[] args)
    {
        var authorsList = new List<Author>()
        {
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=11 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=20 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=14 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Fred", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Trevor", Lastname = "Smith", Age=15 },
            new Author{ Firstname = "Brian", Lastname = "Smith", Age=11 },
            new Author{ Firstname = "Billy", Lastname = "Smith", Age=11 },
        };
        var authorsListExcept = new List<Author>()
        {
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Fred", Lastname = "Smith", Age=12 },
        };
        var authorsList2 = authorsList
            .Except(authorsListExcept, new AuthorUpdatedComparer()).ToList();
    }
}
class Author
{
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public int Age { get; set; }
}
class AuthorUpdatedComparer : IEqualityComparer<Author>
{
    public bool Equals(Author x, Author y)
    {
        return x.Age >= y.Age;
    }
    public int GetHashCode(Author obj)
    {
        //Check whether the object is null 
        if (Object.ReferenceEquals(obj, null)) return 0;
        int FirstnameHash = (obj.Firstname ?? "").GetHashCode();
        int LastnameHash = (obj.Lastname ?? "").GetHashCode();
        int finalResult = FirstnameHash ^ LastnameHash;
        return finalResult;
    }
}

我的作者列表2结果将是：鲍勃·史密斯，20岁* 14岁的Bom Smith特雷弗·史密斯，15岁* 布莱恩·史密斯，11岁* 11岁的比利·史密斯

但取而代之的是不包括 14 岁的鲍勃史密斯。在调试时，我得出的结论是，包括 20 岁的鲍勃史密斯之后的比较器开始使用它有一个比较器，然后排除了鲍勃的年龄小于 20 岁。

在我看来，这是一种奇怪的行为，它应该只排除那些更年轻或与作者列表上的人年龄相同的人ListExcept。我试图阅读msdn文档，我想要它应该发生什么：字体： http://msdn.microsoft.com/en-US/图书馆/BB336390（v=vs.100）.aspx

有人可以帮助我吗？谢谢雨果·萨尔加多

IEqualityComparer上的奇怪行为

以下 LINQ 查询提供所需的结果：

var result = 
    authorsList.GroupBy(x => Tuple.Create(x.Firstname, x.Lastname))
               .SelectMany(g => g.Where(x => authorsListExcept.All(e => e.Firstname != x.Firstname || e.Lastname != x.Lastname || e.Age < x.Age)));

以下查询也会生成此结果。它应该表现得更好：

var result = 
    authorsList.GroupBy(x => Tuple.Create(x.Firstname, x.Lastname))
               .GroupJoin(authorsListExcept, x => x.Key,
                          x => Tuple.Create(x.Firstname, x.Lastname),
                          (a, e) => a.Where(x => x.Age > e.Select(z => z.Age)
                                                          .DefaultIfEmpty(0)
                                                          .Max()))
               .SelectMany(x => x)

第三个选项（与上一个相同，但在查询语法上）：

var result = 
    (from a in authorsList
    group a by Tuple.Create(a.Firstname, a.Lastname) into g
    join e in authorsListExcept on g.Key equals Tuple.Create(e.Firstname, e.Lastname) into er
    from age in er.Select(x => x.Age).DefaultIfEmpty()
    select g.Where(x => x.Age > age)).SelectMany(x => x);

接口IEqualityComparer<T>用于检查相等性。它与任何排序无关。因此，您不能以尝试的方式使用它。

通常：此接口的实现应始终在GetHashCode实现和Equals方法中使用完全相同的属性集。

如果我了解了您想要什么，请尝试此操作。

class Program
{
    static void Main(string[] args)
    {
        var authorsList = new List<Author>()
        {
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=11 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=20 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=14 },
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Fred", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Trevor", Lastname = "Smith", Age=15 },
            new Author{ Firstname = "Brian", Lastname = "Smith", Age=11 },
            new Author{ Firstname = "Billy", Lastname = "Smith", Age=11 },
        };
        var authorsListExcept = new List<Author>()
        {
            new Author{ Firstname = "Bob", Lastname = "Smith", Age=12 },
            new Author{ Firstname = "Fred", Lastname = "Smith", Age=12 },
        };
        var authorsList2 = authorsList.Where(x => !authorsListExcept.Any(y => y.Firstname == x.Firstname && y.Lastname == x.Lastname && x.Age <= y.Age));
    }
}
public class Author
{
    public string Firstname { get; set; }
    public string Lastname { get; set; }
    public int Age { get; set; }
}
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