Question

我在下面的c＃代码片段中总结了我的问题。我通过review来过滤酒店。我们从用户的逗号分隔值中获取用户评论。目前我循环用户评论并将每个结果合并到单一结果。现在，我想将循环和linq查询写入单个linq查询。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace LinqST
{
    public class Hotel
    {

        public string Name { get; set; }
        public int Review { get; set; }

    }
    public class DAL
    {
        public static List<Hotel> Get()
        {
            return new List<Hotel>()
            {
                new Hotel{Name="Hotel1",Review=4},
                new Hotel{Name="Hotel2",Review=2},
                new Hotel{Name="Hotel3",Review=2},
                new Hotel{Name="Hotel4",Review=3},
                new Hotel{Name="Hotel5",Review=5},
                new Hotel{Name="Hotel6",Review=5},
                new Hotel{Name="Hotel61",Review=4},
                new Hotel{Name="Hotel6",Review=4}
            };
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var filterHotel = "3,4";
            var tempList = new List<Hotel>();
            foreach (var item in  Array.ConvertAll(filterHotel.Split(','), s => int.Parse(s)))
            {
                var list = DAL.Get().Where(x => x.Review == item);
                tempList = tempList.Union(list).ToList();
            }
        }
    }
}

Answer 1

尝试使用Contains：

var filteredIds = Array.ConvertAll(filterHotel.Split(','), int.Parse); // or filterHotel.Split(',').Select(int.Parse);
var list = DAL.Get().Where(x => filteredIds.Contains(x.Review));

Answer 2

听起来你有一个加入，基本上是：

var ratings = filterHotel.Split(',').Select(text => int.Parse(text)).Distinct();
var list = DAL.Get()
              .Join(ratings, hotel => hotel.Review, rating => rating,
                    (hotel, rating) => hotel)
              .ToList();

编辑：根据要求，如果单个陈述对您而言比可读性更有价值：

var list = DAL.Get()
              .Join(filterHotel.Split(',').Select(text => int.Parse(text)).Distinct(),
                    hotel => hotel.Review,
                    rating => rating,
                    (hotel, rating) => hotel)
              .ToList();

或者作为查询表达式：

var list = (from hotel in DAL.Get()
            join rating in filterHotel.Split(',')
                                      .Select(text => int.Parse(text))
                                      .Distinct()
            on hotel.review equals rating
            select hotel).ToList();

Answer 3

你可以用这个：

tempList = Array.ConvertAll(filterHotel.Split(','), int.Parse)
                .Select(item => DAL.Get().Where(x => x.Review == item))
                .Aggregate(tempList, (current, list) => current.Union(list).ToList());

结果由resharper

将foreach循环和linq查询组合成单个linq查询

3 个答案: