使用LINQ到实体的内部查询（子查询），返回列表中的IEnumerable列表

Question

我试图从列表中列出文章列出了每篇文章列出的类别列表。说文章“A”有3个类别“1”，“2”，“3”，我有超过一个类别的多个文章。我想获取ArticleViewModel内的CategoryViewModel的列表。因为它是IEnumerableList，所以当我使用FirstOrDefault（）时，我在每篇文章下获得相同的类别名称，但是我获得了正确的文章数量。如何在文章（列表）中获得类别名称（列表）。

ArticleViewModel类

 
    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; } 
    } 

CategoryViewModelClass

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

ArticleCategory

 
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; } 

QUERY

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

好了，过了几天。我意识到这是想让事情过分。我的错 ！修复很简单;在视图模型中将类别更改为IEnumerable<string> Category {get; set;}。

，改变的LINQ to

 
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);