在lambda上执行distinct()时，替换IEquatable接口

Question

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);
}

我需要这个，因为我正在尝试以这种方式返回IEquatable<ArticleDescriptionDetails>：

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

有没有一种方法可以在不使用IEquatable<T>接口的情况下完成同样的事情？

Answer 1

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DistinctBy方法在linq中不存在，但您可以在morelinq包中找到它https://www.nuget.org/packages/MoreLinq.Source.MoreEnumerable.DistinctBy/

但是，编写自己版本的方法也很容易：您首先需要定义一个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);
}