IEqualityComparer

在linq中使用union和distinct都不起作用，结果发现必须传入一个实现了IEqualityComparer<T>的比较器

    public class CompareUser : IEqualityComparer<UserEntity>
    {
        public bool Equals(UserEntity x, UserEntity y)
        {
            if (x == null && y == null)
                return false;
            return x.Initial == y.Initial;
        }

        public int GetHashCode(UserEntity obj)
        {
             return obj.ToString().GetHashCode();
        }
    }