使用LINQ到實體的內部查詢（子查詢），返回列表中的IEnumerable列表

Question

我試圖從列表中列出文章列出了每篇文章列出的類別列表。說文章「A」有3個類別「1」，「2」，「3」，我有超過一個類別的多個文章。我想獲取ArticleViewModel內的CategoryViewModel的列表。因爲它是IEnumerableList，所以當我使用FirstOrDefault（）時，我在每篇文章下獲得相同的類別名稱，但是我獲得了正確的文章數量。如何在文章（列表）中獲得類別名稱（列表）。

ArticleViewModel類

 
    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，過了幾天。我意識到這是想讓事情過分。我的錯 ！修復很簡單;在視圖模型中將類別更改爲IEnumerable<string> Category {get; set;}。

，改變的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);