c# - Linq to Entities Group By 那里有一些没有元素的组

Question

模型类:

public class Video
{
    public int Id { get; set; }
    public string Name { get; set; }
    public DateTime ReleasedDate { get; set; }
    public byte GenreId { get; set; }
    public Genre Genre { get; set; }
    public Classification Classification { get; set; }
    public IList<Tag> Tags { get; set; }
}

public class Genre
{
    public byte Id { get; set; }
    public string Name { get; set; }
    public IList<Video> Videos { get; set; }
}

例如，类型名称是: Action 、戏剧、喜剧和恐怖。没有喜剧和恐怖类型的视频。

查看模型类:

public class CountOfVideos
{
    public string Classification { get; set; }
    public int NumberOfMovies { get; set; }
}

Controller 类:

 public ActionResult Movies()
    {
        var movies = _context.Videos
            .GroupBy(v => v.Genre.Name)
            .Select(g => new CountOfVideos { Classification = g.Key, NumberOfMovies = g.Count() })
            .ToList();

        return View(movies);
    }

查看:

@model IEnumerable<LinqTest.ViewModels.CountOfVideos>

<table class="table table-bordered table-hover">
<thead>
    <tr>
        <th>Name</th>
        <th>Count</th>
    </tr>
</thead>
<tbody>
    @foreach (var movie in Model)
    {
        <tr>
            <td>@movie.Classification</td>
            <td>@movie.NumberOfMovies</td>
        </tr>
    }
</tbody>

代码工作正常，但它不显示其中没有视频的流派名称。 View 生成如下内容:

行动 23戏剧15但我想生成 Action 23 Drama 15 Comedy 0 Horror 0。

Answer 1

您应该从包含所需基础数据的集合开始。在这种情况下:流派。

类似于:

 public ActionResult Movies() {
  var genres = _context.Genres
   .Select(g => new CountOfVideos {
    Classification = g.Name, NumberOfMovies = g.Videos.Count()
   })
   .OrderBy(c => c.NumberOfMovies)
   .ToList();

  return View(genres);
 }