Question

我在C＃中非常陌生，我想在Linq.plz帮助中编写此TSql代码。谢谢

select a.Id,
       a.Date,
       b.Title CategoryTitle,
       a.Title,
       a.Description,
       a.Image 
  from (select *, 
               ROW_NUMBER() over(partition by CategoryID order by Date) rankno 
          from News) a
  join Categories b on a.CategoryID = b.Id
 where rankno <= 5

Answer 1

假设您有新闻和类别的枚举：

var results = News.Join(Categories,         // Join News and Categories
                        a => a.CatergoryId, 
                        b => b.Id, 
                        (a,b) => new { News = a, Category = b}
                    )  
    .GroupBy(c => c.Category) // "partition by categoryId"
    .SelectMany(g => g.OrderBy(gd => gd.News.CreationDate)   // "order by Date"
                        .Take(5)    // RankNo <= 5
                        .Select(gdd => new {            // results
                                Id = gdd.News.Id, 
                                Date = gdd.News.Date, 
                                CategoryTitle = gdd.Category.Title,
                                Title = gdd.News.Title,
                                Description = gdd.News.Description, 
                                Image = gdd.News.Image
                            })
                );

Answer 2

我使用类为您的数据库建模，以使语法正确。参见下面的代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace ConsoleApplication93
{
    class Program
    {

        static void Main(string[] args)
        {
            Context dbContext = new Context();

            var results = (from n in dbContext.news 
                           join c in dbContext.category.OrderBy(x => x.Date) on n.Id equals c.Id 
                           select new { news = n, category = c})
                           .Select((x,i) => new { Date = x.news.Date, CategoryTitle = x.category.Title, Title = x.news.Title, Description = x.news.Description, Image = x.news.Image, RankNo = i})
                           .ToList();


        }
    }

    public class Context
    {
        public List<News> news { get; set; }
        public List<Category> category { get; set; }
    }
    public class News
    {
        public int Id { get; set; }
        public DateTime Date { get; set; }
        public string Title { get;set;}
        public string Description { get;set;}
        public byte[] Image { get;set;}

    }
    public class Category
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public DateTime Date { get; set; }
    }

}

连接和分区方式中的嵌套选择

2 个答案: