C#-Linq扩展方法DistinctBy

public static class LinqExtensions
    {
        public static IEnumerable<T> DistinctBy<T, TKey>(this IEnumerable<T> items, System.Func<T, TKey> property)
        {
            GeneralPropertyComparer<T, TKey> comparer = new GeneralPropertyComparer<T, TKey>(property);
            return items.Distinct(comparer);
        }
    }
    public class GeneralPropertyComparer<T, TKey> : IEqualityComparer<T>
    {
        private System.Func<T, TKey> expr { get; set; }
        public GeneralPropertyComparer(System.Func<T, TKey> expr)
        {
            this.expr = expr;
        }
        public bool Equals(T left, T right)
        {
            var leftProp = expr.Invoke(left);
            var rightProp = expr.Invoke(right);
            if (leftProp == null && rightProp == null)
                return true;
            else if (leftProp == null ^ rightProp == null)
                return false;
            else
                return leftProp.Equals(rightProp);
        }
        public int GetHashCode(T obj)
        {
            var prop = expr.Invoke(obj);
            return (prop == null) ? 0 : prop.GetHashCode();
        }
    }

自带的Distinct能做的事比较简单，对比集合中的Object的Hash值来去重

很多时候我们需要的是根据Object中的某个字段值来做去重，比如Student.Name

那么自带的Distinct就要自己实现一个Comparer了

找了很多资料，发现有前人种下了这棵树，分享出来。

Usage：{Linq代码}.DistinctBy(Student.Name).ToList();