LINQ to Entities does not recognize the method 'System.Threading.Tasks.Task`

Question

How can I solve this problem?

An exception of type 'System.NotSupportedException' occurred in EntityFramework.SqlServer.dll but was not handled in user code

Additional information: LINQ to Entities does not recognize the method 'System.Threading.Tasks.Task`1[Jahan.Blog.Model.Identity.User] FindByIdAsync(Int32)' method, and this method cannot be translated into a store expression.

 public virtual User User { get; set; }
 private IQueryable<ArticleGridViewModel> Query()
 {
    ArticleRepository repository = new ArticleRepository();
    IQueryable<ArticleGridViewModel> query = repository.FindAll().Select(article => new     ArticleGridViewModel
    {
       Tags = article.ArticleTags.Where(c => c.ArticleId == article.Id).Select(b => b.Tag).Distinct().ToList(),
       NumberOfComments = article.Comments.Count(c => c.ArticleId == article.Id),
       AttachmentFiles =article.AttachmentFiles.Where(a => a.ArticleId == article.Id).Distinct().ToList(),
       CreatedDate = article.CreatedDate,
       IsActive = article.IsActive,
       IsActiveNewComment = article.IsActiveNewComment,
       LikeCounter = article.LikeCounter,
       ModifiedDate = article.ModifiedDate,
       RateCounter = article.RateCounter,
       Title = article.Title,
       UserId = article.UserId,
       Comments = Comments.Where(c => c.ArticleId == article.Id).ToList(),



       User = AppUserStore.Instance.FindByIdAsync(article.Id).Result, // The error happened because of this line of code.

   });
   return query;
 }

 public virtual IQueryable<ArticleGridViewModel> QueryByCriteria(Expression<Func<ArticleGridViewModel, bool>> predicate = null, params Expression<Func<ArticleGridViewModel, object>>[] includeProperties)
    {
        IQueryable<ArticleGridViewModel> items = Query();
        if (includeProperties != null)
        {
            foreach (var includeProperty in includeProperties)
            {
                items = items.Include(includeProperty);
            }
        }
        if (predicate != null)
            return items.Where(predicate);
        return items;
    }
    public virtual IEnumerable<ArticleGridViewModel> FindAll(Expression<Func<ArticleGridViewModel, bool>> predicate = null, params Expression<Func<ArticleGridViewModel, object>>[] includeProperties)
    {
        List<ArticleGridViewModel> result = QueryByCriteria(predicate, includeProperties).ToList();
        return result;
    }

Answer 1

Everything inside of that .Select(x=>) statement must be able to be converted to a SQL expression. That is why trying to use .ToString() (an example) can fail with the same error in some instances.

Basically, EF has no idea how to translate an object of System.Threading.Tasks.Task to a SQL statement.

Given you are trying to call this with values retrieved from the query, you will most likely need to either

1. Loop over the results from the .Select() method and run this function for each result to set the User property or,
2. Implement the logic yourself in that line as opposed to calling a function, like you have in other places with your where clauses.