在lambda上执行distinct时，替代IEquatable接口

如何解决在lambda上执行distinct时，替代IEquatable接口

我有一个实现IEquatable<T>接口的类

public class ArticleDescriptionDetails : IEquatable<ArticleDescriptionDetails>
{
    public string Code { get; set; }
    public string Value { get; set; }
    public bool Hidden { get; set; }

    public bool Equals(ArticleDescriptionDetails other)
    {
        if (ReferenceEquals(null,other)) return false;
        if (ReferenceEquals(this,other)) return true;
        return Code == other.Code;
    }

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null,obj)) return false;
        if (ReferenceEquals(this,obj)) return true;
        return obj.GetType() == GetType() && Equals((ArticleDescriptionDetails) obj);
    }

    public override int GetHashCode() => ((Code != null ? Code.GetHashCode() : 0) * 397) ^ Hidden.GetHashCode();

    public static bool operator ==(ArticleDescriptionDetails left,ArticleDescriptionDetails right) => Equals(left,right);

    public static bool operator !=(ArticleDescriptionDetails left,ArticleDescriptionDetails right) => !Equals(left,right);
}

我需要这样做是因为我正试图以这种方式返回IEquatable<ArticleDescriptionDetails>：

return result.OrderBy(x => x.Code).ThenBy(y => y.Hidden).distinct();

是否有一种无需使用IEquatable<T>界面即可完成相同操作的方法？

解决方法

您可以使用DistinctBy方法并执行

return result.OrderBy(x => x.Code).ThenBy(y => y.Hidden).DistinctBy(z => z.Code); 

但是linq中不存在DistinctBy方法，但是您可以在morelinq软件包https://www.nuget.org/packages/MoreLinq.Source.MoreEnumerable.DistinctBy/

中找到它

但是编写自己的方法版本也很容易： 您首先需要定义IEqualityComparer

    public class KeyEqualityComparer<T,K> : IEqualityComparer<T>
    {
        private readonly Func<T,K> selector;

        public KeyEqualityComparer(Func<T,K> keySelector)
        {
            selector = keySelector;
        }

        public bool Equals(T x,T y)
        {
            return selector(x).Equals(selector(y));
        }

        public int GetHashCode(T obj)
        {
            return selector(obj).GetHashCode();
        }
    }

您可以在Distinct方法中使用此IEqualityComparer：

        public static IEnumerable<T> DistinctBy<T,K>(this IEnumerable<T> list,Func<T,K> keySelector)
        {
            var equalityComparer = new KeyEqualityComparer<T,K>(keySelector);
            return list.Distinct(equalityComparer);
        }