使用LINQ to实体的内部查询（子查询），在列表中返回IEnumerable列表

Question

我试图从表文章列表的文章与类别列表，每篇文章是列出的。假设文章“A”有3个类别“1”，“2”，“3”，我有一个以上的文章有一个以上的类别。我想在ArticleViewModel的列表中获得CategoryViewModel的列表。因为它是IEnumerableList，所以当我使用FirstOrDefault（）时，我会在每个文章下获得相同的类别名称，但获得的文章数量是正确的。我如何才能获得类别名称（列表）内的文章（列表）。

    public class ArticleViewModel
    {
        public int ArticleID { get; set; }
        public int AuthorID { get; set; }
        public string AuthorName { get; set; }
        public string Username { get; set; }
        public string Slug { get; set; }
        public string Title { get; set; }
        public string ArticleContent { get; set; }
        public DateTime PostDate { get; set; }
        public Nullable UpdatedDate { get; set; }
        public int ArticleCategoryID { get; set; }
        public int CategoryID { get; set; }
        public IEnumerable CategoryNames { get; set; }
        public int TagID { get; set; }
        public string TagName { get; set; }
    }

    public class CategoryViewModel
    {
        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
    }

 public partial class ArticleCategory
    {
        public int ArticleCategoryID { get; set; }
        public int ArticleID { get; set; }
        public int CategoryID { get; set; }

        public virtual Article Article { get; set; }
        public virtual Category Category { get; set; }

查询

result = (from articles in db.Articles
                join articlecategories in db.ArticleCategories on articles.ArticleID equals articlecategories.ArticleID
                join cat in db.Categories on articlecategories.CategoryID equals cat.CategoryID
                join auth in db.Authors on articles.AuthorID equals auth.AuthorID
                select new ArticleViewModel
                {
                    AuthorName = auth.AuthorName,
                    Username = auth.UserName,

                    CategoryNames = (from a in db.Articles
                                    //from ca in db.ArticleCategories
                                    //from c in db.Categories group c by c.CategoryName into group1
                                    join ca in db.ArticleCategories on articlecategories.ArticleID equals ca.ArticleID
                                    join c in db.Categories on cat.CategoryID equals c.CategoryID into group1                                               
                                    select new CategoryViewModel
                                    {                                                  
                                        CategoryName = (from group2 in group1 select group2.CategoryName).FirstOrDefault()
                                    //   CategoryID = (from group2 in group1 select group2.CategoryID).FirstOrDefault()
                                    }),

                    Title = articles.Title,
                    Slug = articles.Slug,
                    ArticleContent = articles.ArticleContent,
                    PostDate = articles.PostDate
                }).GroupBy(a => a.Title).Select(a => a.FirstOrDefault()).OrderByDescending(article => article.PostDate).ToList().ToPagedList(pageIndex, pageSize);

Answer 1

好吧，过了几天。我意识到这是试图把事情做过头。我的错！修复很简单；在视图模型中将类别更改为IEnumerable 类别{get；set；} 。

并将LinQ更改为

result = (from articles in db.Articles
                              join articlecategories in db.ArticleCategories on articles.ArticleID equals articlecategories.ArticleID
                              join cat in db.Categories on articlecategories.CategoryID equals cat.CategoryID
                              join auth in db.Authors on articles.AuthorID equals auth.AuthorID
                              join tags in db.ArticleTags on articles.ArticleID equals tags.ArticleID

                              select new ArticleViewModel
                              {
                                  ArticleID=articles.ArticleID,
                                  AuthorName = auth.AuthorName,
                                  Username = auth.UserName,
                                  Title = articles.Title,
                                  Slug = articles.Slug,
                                  ArticleContent = articles.ArticleContent,
                                  PostDate = articles.PostDate,
                                  CategoryNames = from icat in articles.ArticleCategories select icat.Category.CategoryName,
                                  Tags = from itags in articles.ArticleTags select itags.Tag.TagName

                              }).GroupBy(a => a.Title).Select(a => a.FirstOrDefault()).ToPagedList(pageIndex, pageSize);