使用 Linq 加入、分组和计数....面临一个麻烦

Question

我的数据库中有两个表，picture 和 pictureratings。

public partial class picture
{
    public int idpicture { get; set; }
    public int iduser { get; set; }
    public string picTitle { get; set; }
    public string picFilename { get; set; }
    public System.DateTime pictime { get; set; }
    public int nuditylevel { get; set; }
    public int fakeslevel { get; set; }

    // This property will hold the total accumulated/summed 
    // up rating of a picture
    public int totalrating { get; set; }    
}

public partial class pictureratings 
{
    public int idrating { get; set; }
    public int idpictures { get; set; }
    public int iduser { get; set; }
    public System.DateTime iddatetime { get; set; }
    public int iduserrateddby { get; set; }
    public int rating { get; set; } 
}

对于每个评分，都会创建一个新的pictureratings 行。我想按图片 ID 对 pictureratings 表进行分组，然后计算点赞数。我想在totalrating 属性的picture 表中显示这些喜欢。

所以根据我目前的研究，我可以编写这段代码

var total = from p in db.picturedetails
            join l in db.picturelikes on p.idpictures equals l.idpictures 
            group l by l.idpictures into g
            select new 
            {
                IdUserPic = g.First().iduser,
                IdPictures = g.First().idpictures,
                totalrating = g.Count()    
            }

我正在使用 web api 返回查询总数。所以我的问题来了：如何显示picture 属性，如iduser、picTitle、picFilename、pictime、nuditylevel 和fakeslevel？我做对了吗？我该怎么做？

Answer 1

您可以对匿名类进行分组。这样您就可以同时访问 p & l 属性。
看起来像这样：

var total = from p in db.picturedetails
            join l in db.picturelikes on p.idpictures equals l.idpictures 
            group new {p,l} by l.idpictures into g
            select new 
            {
                IdUserPic = g.First().p.iduser,
                IdPictures = g.First().p.nuditylevel,
                totalrating = g.Count()    
            }

Answer 2

我认为group join 是您正在寻找的：

var total = from p in db.picturedetails
            join l in db.picturelikes on p.idpicture equals l.idpictures into pl
            select new
            {
                Picture = p,
                AverageRating = pl.Any()
                                    ? pl.Average(l => l.rating)
                                    : (double?)null,
                RatingsCount = pl.Count(),
                TotalRating = pl.Sum(l => (float?)l.likenumber) ?? 0
            };

如果一张图片没有点赞，这将为该图片提供0 总数和null 平均值。