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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要完成的工作：

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
            .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 authorsList2 结果是：* Bob Smith 20 岁 * Bom Smith 14 岁 * Trevor Smith 15 岁 * Brian Smith 11 岁 * Billy Smith 11 岁

但取而代之的是 14 岁的 Bob Smith 不包括在内。在调试时，我得出的结论是，包含 Bob Smith 和 20 岁开始使用它的比较器有一个比较器，排除了所有 Bob 小于 20 岁的比较器。

在我看来，这是一种奇怪的行为，它应该只排除那些年龄较小或与作者列表中包含的人相同年龄的人。我试图阅读 msdn 文档，我希望它应该发生：字体： http: //msdn.microsoft.com/en-us/library/bb336390 (v=vs.100).aspx

任何人都可以帮助我吗？谢谢，雨果萨尔加多

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2 回答 2

1

以下 LINQ 查询提供了您期望的结果：

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)));

以下查询也会产生此结果。它应该表现更好：

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（与前一个相同，但在查询语法中）：

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);

该接口IEqualityComparer<T>用于检查是否相等。它与任何排序无关。因此，您不能以您尝试的方式使用它。

GetHashCode通常：此接口的实现应始终在实现和Equals方法中使用完全相同的一组属性。

于 2013-09-19T15:01:43.997 回答
0

如果我明白你想要什么试试这个。

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; }
}
于 2013-09-19T15:36:23.043 回答