linq to sql -> join

Question

SQL query:

SELECT     ArticleCategories.Title AS Category, Articles.Title, Articles.[Content], Articles.Date
FROM         ArticleCategories INNER JOIN
                   Articles ON ArticleCategories.CategoryID = Articles.CategoryID

Object repository:

public class ArticleDisplay
    {
        public int CategoryID;
        public string CategoryTitle;

        public int ArticleID;
        public string ArticleTitle;
        //public string ArticleDate;
        public string ArticleContent;
    }    


public class ArticleRepository
    {
        private DB db = new DB();
        //
        // Query Methods
        public IQueryable<ArticleDisplay> FindAllArticles()
        {
            var result =   from category in db.ArticleCategories
                           join article in db.Articles on category.CategoryID equals article.CategoryID
                           select new
                           {
                               CategoryID = category.CategoryID,
                               CategoryTitle = category.Title,

                               ArticleID = article.ArticleID,
                               ArticleTitle = article.Title,
                               //ArticleDate = article.Date,
                               ArticleContent = article.Content
                           };

            return result;

        }
        ....
    }

And finally, I get this error:

Error 1 Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Linq.IQueryable'. An explicit conversion exists (are you missing a cast?) C:\Documents and Settings\ilija\My Documents\Visual Studio 2008\Projects\CMS\CMS\Models\ArticleRepository.cs 29 20 CMS

Any idea what did I do wrong?

Thanks,
Ile

Answer 1

Your method has a return type of IQueryable<Article>, but your LINQ query is not returning articles. Instead it's trying to return an anonymous type made up of properties from both category and article. You could create a class to hold this combination of properties and change the method signature to use that class.

Answer 2

As Adam said, if you're not wanting to return the full article class then you'll need to return your own class.

public IQueryable<ArticleDisplay> FindAllArticles()
    {
        var result =   from category in db.ArticleCategories
                       join article in db.Articles on category.CategoryID equals article.CategoryID
                       select new ArticleDisplay() //specify your new class
                       {
                           CategoryID = category.CategoryID,
                           CategoryTitle = category.Title,
                           ....
                       };

        return result;

    }

Your updated code still returns an anonymous class....