Question

intHi，

LINQ很新。

我有一张评级表用户为实体添加一组评级每个用户的实体可以有多个评级集。

例如，假设实体是一辆汽车。该车的外观和性能评级。用户可以不止一次评估给定汽车的外观和性能。所以我的表看起来像这样（评级字段不是一个标识列;它是一个比例为1 - 10的int）：

ReviewID     UserID     EntityID     CatID     Rating    Body               DateSubmitted
1            3          6            1         7         "drives great"     8/01/2010 02:36:28 PM
2            3          6            2         8         "looks great"      8/01/2010 02:36:28 PM
3            3          6            1         2         "broke down"       8/18/2010 11:39:58 PM
4            3          6            2         1         "paint flaked off" 8/18/2010 11:39:58 PM

现在，我有一个帮助方法，我提供UserID和EntityID，我想返回最新的评级集（进入包含评级类别的ViewModel）。

public static IQueryable<RatingViewModel> GetRatingViewModel(int EntityID, int UserID)
    {
        DB _db = new DB();

        var a =

            from rating in _db.Ratings
            join ratingCat in _db.RatingCategories
                on rating.RatingCategoryID equals ratingCat.RatingCategoryID
            where rating.UserID == UserID
                && rating.EntityID == EntityID
            select new RatingViewModel
             {
                 Rater = rating.User,
                 RaterRating = rating,
                 RatingCategory = ratingCat

             };

        return a;
    }

我需要添加什么样的“where”或“group by”或“order by”才能获取给定UserID和EntityID的最新评级集？

谢谢！

Answer 1

考虑通过DateSubmitted对方法的返回进行排序，然后获取您想要的条目数。

var a = from rating in _db.Ratings
        join ratingCat in _db.RatingCategories
            on rating.RatingCategoryID equals ratingCat.RatingCategoryID
        where rating.UserID == UserID
            && rating.EntityID == EntityID
        orderby rating.DateSubmitted descending

        select new RatingViewModel
         {
             Rater = rating.User,
             RaterRating = rating,
             RatingCategory = ratingCat

         }
         .Take(10);

Answer 2

.OrderByDescending(a => a.DateSubmitted).FirstOrDefault()

LINQ to SQL，获取给定ID的最新记录

2 个答案: